Any time counsel fails to provide effective representation trial fairness suffers and may result in a miscarriage of justice.
The proper test for overturning a verdict due to ineffectiveness of counsel requires that: 
- the "counsel's performance was deficient" such that counsel made serious errors; and
- the "deficient" performance prejudiced the defence in a way that deprived the accused of a fair trial.
A claim for ineffective assistance or incompetent counsel has two components. There must be performance that is incompetent (performance component) and the performance must result in a "miscarriage of justice" (the prejudice component).  Thusly, the applicant must prove:
- the facts that underpin the claim on a balance of probabilities;
- the act or omission that was believed to be incompetent assistance by counsel;
- the incompetent assistance caused a miscarriage of justice by undermining either appearance of a fair trial or reliability of the verdict.
Absent a possible injustice flowing from the incompetency of counsel there can be no appeal. 
Principles of Fundamental Justice
The "principles of fundamental justice" under section 7 of the Charter include the "right to effective assistance of counsel" in the criminal justice system.
Burden and Standard of Proof
The onus is upon the accused. There is a strong presumption in favour of competence.
The applicant must prove all elements that make up a finding of ineffective counsel on a standard of balance of probabilities.
R v GDB,  1 SCR 520, 2000 SCC 22 (CanLII) at para 1
R v Garofoli, 1988 CanLII 3270 (ONCA)
R v Schofield (G.R.) 1996 CanLII 8709 (NSSC)
R v Strauss (D.W.), 1995 CanLII 702 (BCCA)
Adopted from the US case of Strickland v Washington, 104 S. Ct. 2052 (1984) ("A convicted defendant’s claim that counsel’s assistance was so defective as to require reversal of a conviction ...has two components. First, the defendant must show that counsel’s performance was deficient. This requires showing that counsel made errors so serious that counsel was not functioning as the ‘counsel’ ... . Second, the defendant must show that the deficient performance prejudiced the defense. This requires showing that counsel’s errors were so serious as to deprive the defendant of a fair trial, a trial whose result is reliable. Unless a defendant makes both showings, it cannot be said that the conviction or death sentence resulted from a breakdown in the adversary process that renders the result unreliable.”)
- Garofoli, supra
- Schofield, supra
- Strauss, supra
R v Gardiner, 2010 NBCA 46 (CanLII) at para 2
R v Archer, 2005 CanLII 36444 (ON CA), per Doherty JA, at para 119
R v G(DM), 2011 ONCA 343 (CanLII) at para 100
R v B(J) 2011 ONCA 404 (CanLII) at para 2
R v Le (T.D.), 2011 MBCA 83 (CanLII) at para 178
R v Kim, 2011 SKCA 74 (CanLII)
R v Joanisse 1995 CanLII 3507 (ON CA), (1995), 102 CCC (3d) 35 (ONCA), at para 69 leave to appeal refused,  S.C.C.A. No. 347
R v White 1997 CanLII 2426 (ON CA), (1997), 99 OAC 1 at paras 63-65, 114 CCC (3d) 225; leave to appeal denied, 117 CCC (3d) vi (SCC)
R v Eroma, 2013 ONCA 194 (CanLII)
R v B(M), 2009 ONCA 524 (CanLII), at paras 8-9
R v Rockwood (1989), CanLII 197 (NS CA), 91 N.S.R.(2d) 305; 233 A.P.R. 305 (C.A.) ("The appellant who contends that he has not received this protection must therefore establish: (a) that counsel at the trial lacked competence, and (b) that it is reasonably probable that but for such lack of competence, the result of the proceedings would have been different.")
R v White, 2016 NSCA 20 (CanLII) at para 52 ("an appellant must show that his counsel's acts or omission were incompetent and that a miscarriage of justice resulted")
- Le, supra at para 258
- R v Ensor,  1 W.L.R. 497 (C.A.), Lord Lane, C.J.
R v GDB,  1 SCR 520, 2000 SCC 22 (CanLII), at para 24, ("Today the right to effective assistance of counsel extends to all accused persons. In Canada that right is seen as a principle of fundamental justice. It is derived from the evolution of the common law, s. 650(3) of the Criminal Code of Canada and ss. 7 and 11(d) of the Canadian Charter of Rights and Freedoms.")
R v LW, 2006 CanLII 7393 (ON CA),  O.J. No. 955 at para 50
GDB, supra at para 27 ("Incompetence is determined by a reasonableness standard. The analysis proceeds upon a strong presumption that counsel’s conduct fell within the wide range of reasonable professional assistance. The onus is on the appellant to establish the acts or omissions of counsel that are alleged not to have been the result of reasonable professional judgment. The wisdom of hindsight has no place in this assessment.")
R v Dunbar, 2003 BCCA 667 (CanLII) at para 24 ("...the appellant must establish, on a balance of probabilities, both that the representation provided by trial counsel was incompetent and that the incompetent representation resulted in a miscarriage of justice. The appellant must draw the link between the alleged incompetence and the prejudice suffered")
Miscarriage of Justice
A miscarriage of justice can either be a a produce of procedural unfairness or an unreliable result.
Most instances of miscarriage of justice will be based on "unreliable verdict".
Unreliability requires that the appellant show that there was "a reasonable possibility that, but for the incompetence, the verdict could have been different".
Procedural unfairness arises where counsel has "made certain decisions that should have been made by the accused person". This usually relates to the core parts of the proceedings that relate to the accused's "fundamental rights to control his or her own defence". Those fundamental rights consist of:
- how to plead;
- waiver of the right to a jury trial; and
- whether to testify.
R v GDB,  1 SCR 520, 2000 SCC 22 (CanLII) at para 28 ("Miscarriages of justice may take many forms in this context. In some instances, counsel's performance may have resulted in procedural unfairness. In others, the reliability of the trial's result may have been compromised.")
R v Stark, 2017 ONCA 148 (CanLII) at para 14
Stark, ibid. at para 15
Stark, ibid. at para 15
Stark, ibid. at para 16
R v Swain, 1991 CanLII 104 (SCC),  1 S.C.R. 933, at para. 35
Stark, supra at para 17
The claimant will usually need to adduce fresh evidence by affidavit or oral testimony that sets out the deficiencies in trial counsel. The trial counsel will then be permitted to respond to the allegations. 
A court should not "blindly" accept an appellant's affidavit of evidence without any evidence from the trial counsel or trial record suggesting something is wrong.
Unless the transcript confirms the allegations, the appeal counsel should present evidence from trial counsel. Where the transcript raises concerns of competence, the court should order evidence be taken from the trial counsel. If the court is satisfied from the surrounding circumstances and trial transcript that there is no valid concern, then the court can dismiss the appeal at a preliminary stage for failing to establish a factual foundation. In effect, a affidavit from the appellant does not necessarily establish a prima facie case. 
Some courts of appeal have protocols for handling appeals on incompetent counsel.
Decisions of Counsel
Failure to Testify
Counsel's disregard of the accused's choice on whether to testify will generally result in a miscarriage of justice. Where it is established that the accused would have testified except for the refusal of counsel to let him do so would be a miscarriage. The key element is the finding of whether the accused actually would have testified but for the advice.
Simply advising against testifying without making the choice for the accused will not be enough.
Where it is in dispute that counsel made the choice for the accused not to testify, there is presumption that counsel know
Evidence such as the likely damage to the accused's case should they have testified can go to the assessment of credibility.
Counsel's refusal to listen to instructions by accused to testify at trial has a strong likelihood of resulting in a miscarriage of justice.
R v Archer, 2005 CanLII 36444 (ON CA) at para 139 per Doherty JA
R v GDB,  1 SCR 520, 2000 SCC 22 (CanLII) at para 34
- See R v Eroma, 2013 ONCA 194 (CanLII)
- e.g. see R v Benham, 2013 BCCA 276 (CanLII)
e.g. R v Qiu, 2010 ONCA 736 (CanLII) - accused claimed to not understand decision due to poor interpreter
R v WEB, 2012 ONCA 776 (CanLII) - lawyer recommended and client agreed at the time not to testify
- Qiu, supra at para 15
- Eroma, supra
Tactics and Strategy
The Courts are generally deferential to counsel in their conduct and given them wide latitude with defence strategy. It is understood that different defence counsel will use different trial strategies and tactics, all of which are reasonable. No two lawyers will defend a case in the same way. The art of advocacy is is "highly individualized".
Counsel has "implied authority" to make tactical decisions on behalf of the accused.
Appellants are not entitled to a new trial simply "to see if a different tactic will work better".
Reviewing courts should not be engaging in "Monday morning quarterbacking" upon the trial tactics chosen.
It is a misapprehension of counsel's role to advance all evidence and argument suggested by the accused or to obtain approval before taking action in trial.
The accused is not entitled to any control over the form of the examinations done by counsel.
In some situations, the refusal to interview proposed defence witnesses may lead to a miscarriage.
Where experienced accused is aware of deficiencies of counsel and yet expressed satisfaction with counsel, it may lead to finding that the accused intentionally set it up as a ground of appeal.
A refusal to seek a challenge for cause at the jury selection after the accused reasonably raises the need for it can be a denial of the "statutory right to challenge potential jurors".
Quality of Examinations
It is recognized that a cross-examination is a difficult component of trial work and "slips" will occur. There are also a wide variety of legitimate techniques and approaches.
Relevant to the reviewing court's consideration is the trial counsel's explanation for the strategy for the examination.
A mere failure to cross-examine certain witnesses, without more, is speculative of whether examination would have changed the outcome.
An examination that does not satisfy the Rule in Brown v Dunn which results in the defence being prevented from adducing contradictory evidence can be a miscarriage. Similarly, a failure to cross a complainant on the issues of trial while instead focusing on "peripheral" matters may cause a miscarriage.
Counsel who neglects or refuses to use prior statements to cross examine the complainant on a credibility-based case can be found to breach his duty of competence.
Inappropriate concessions, especially when against instructions of accused, may raise a miscarriage. For example, the failure to object to the playing of a recorded statement of the accused which contained bad character evidence can be enough. There can also be problems agreed to admission of prejudicial voir dire evidence.
R v Kelly 52 O.A.C. 241 (ONCA)(*no CanLII links)
R v Jim,  BCJ No. 1663 (Q.L.)(C.A.)
R v LW, 2006 CanLII 7393 (ON CA),  O.J. No. 955 at para 50
R v GBD,  1 SCR 520, 2000 SCC 22 (CanLII) at para 35
R v Meer, 2015 ABCA 141 (CanLII), at para 32
R v Lomage, (1991) 2 OR (3d) 621 (CA) at para 17
R v SGT,  1 SCR 688, 2010 SCC 20 (CanLII) at para 36
R v LCT, 2012 ONCA 116 (CanLII), at para 54
R v DiPalma,  OJ No 2684 (ONCA)
R v Samra, 1998 CanLII 7174 (ON CA), (1998), 129 CCC (3d) 144 (ONCA)
R v Faulkner, 2013 ONSC 2373 (CanLII)
- e.g. R v Fraser, 2011 NSCA 70 (CanLII)
Meer, supra at para 33 to 34
Fraser, supra at paras 59 to 76
R v White (1997) 114 CCC (3d) 225 (ONCA) at para 116
White, ibid. at para 116
R v RL, 2013 ONCA 504 (CanLII)
R v Dugas, 2012 NSCA 102 (CanLII)
- R v Gardiner, 2010 NBCA 46 (CanLII)
R v JB, 2011 ONCA 404 (CanLII)
R v Schmerl,  O.J. No. 4358
R v Close, 2005 NSSC 351 (CanLII), - counsel failed to use a letter for impeachment of complainant on case of domestic violence.
- R v Loi, 2013 ONSC 1202 (CanLII)
- R v Michaud, 2011 NBCA 74 (CanLII)
- R v Smith, 2007 SKCA 71 (CanLII)
Where counsel's performance is at issue, the applicant must establish that his conduct fell outside of the "wide range of reasonable professional assistance" and that there was "a reasonable possibility that the result at trial would have been different but for his counsel's alleged mistakes".
A failure to review the facts of the case and the accused's version of events until the day of trial can be a factor affecting trial fairness.
Lack of Preparation
A lack of preparation can result in a miscarriage of justice where counsel ends up failing to properly challenge the Crown's case.
Counsel cannot excuse the lack of preparation on account of the limited legal aid hours given.
Ignored or Overlooked Evidence
Counsel who failed to interview a treating doctor to a head injury shortly prior to giving a confession resulted in a miscarriage of justice.
A failure to bring evidence supporting a Carter defence.
R v Joanisse,  O.J. No. 2883, 1995 CanLII 3507 (ON CA), at paras 71, 79-80
- R v Joanisse, 1995 CanLII 3507 (ON CA) at pp. 60-61 per Doherty JA
R v LW, 2006 CanLII 7393 (ON CA),  O.J. No. 955, at para 50
R v IBB, 2009 SKPC 76 (CanLII) at paras 64 to 73 per Whelan PCJ
R v JL, 2016 ONCA 221 (CanLII) at para 12
R v DMG, 2011 ONCA 343 (CanLII)
e.g. R v Smith, 2007 SKCA 71 (CanLII) at para 26
- R v Carr, 2010 ABCA 386 (CanLII)
- R v Critchlow, 2011 ONSC 5177 (CanLII)
Informing the Client
Defence counsel's "failure to advise an accused about the available mode of trial may constitute incompetence leading to a miscarriage of justice in the appropriate case."
Preparing client to what to expect when testifying is a necessary step in informing the client on the process and should be done at a time that "reasonably coincide[s]" with the trial itself.
R v Chica, 2016 ONCA 252 (CanLII) at para 19
R v Stark, 2017 ONCA 148 (CanLII), ("the right to elect the mode of trial under s 536 of the Criminal Code is one of those fundamental rights that counsel cannot take from a client and on which the client is entitled to be adequately advised by counsel.")
R v Simpson, 2018 NSCA 25 (CanLII) at para 46
The failure to properly prepare for trial or develop a strategy while the client maintains his innocence before counsel entered into a plea agreement can amount to a miscarriage of justice due to lack of competence.
Claims of being pressured by counsel should be subject to cross-examination and consideration of credibility.