A mistrial is a remedy where it "is necessary to prevent a miscarriage of justice". A miscarriage can arise where "a trial is unfair, or when the trial has the appearance of unfairness, viewed by a well-informed, reasonable person considering the whole of the circumstances". It will also arise where there is an apprehension of bias.
Pre-Condition to a Mistrial
A declaration of a mistrial "should only be granted as a last resort, in the clearest of cases and where no remedy short of that relief will adequately redress the actual harm occasioned." In a jury trial, a mistrial can only be ordered if the prejudice cannot be remedied by a jury instruction. The decision to grant an application for a mistrial is discretionary.
An appellate court should only intervene where the decision "is so clearly wrong as to amount to an injustice". 
For an application for a mistrial the test is "whether the appellant’s ability to make full answer and defence has been impaired." 
Other remedies, such as mid-trial instructions, should be considered before a mistrial is granted.
Consequence of Mistrial on Future Matters
Where a mistrial is declared, the rulings on pre-trial motions will generally still apply if the prosecution is re-initiated. This section is considered a "departure from previous authority from the Supreme Court of Canada to the effect that a trial judge is not bound by interlocutory rulings made at an earlier trial".
Scheduling of a Re-Trial
A retrial should be scheduled "without further delay". Only a "short period" of delay will be expected. Anything longer may open the possibility of a s. 11(b) Charter delay.
Section 653.1 states:
Mistrial — rulings binding at new trial
653.1 In the case of a mistrial, unless the court is satisfied that it would not be in the interests of justice, rulings relating to the disclosure or admissibility of evidence or the Canadian Charter of Rights and Freedoms that were made during the trial are binding on the parties in any new trial if the rulings are made — or could have been made — before the stage at which the evidence on the merits is presented.
2011, c. 16, s. 14.
R v Burke 2002 SCC 55 (CanLII) at para 75
see also R v Chiasson, 2009 ONCA 789 (CanLII)
R v Toutissani, 2007 ONCA 773 (CanLII),  O.J. No. 4364
R v Khan, 2001 SCC 86 (CanLII), per Arbour J, at para 27
R v Vader, 2016 ABQB 625 (CanLII) at para 10
R v Burke, 2002 SCC 55 (CanLII), per Major J, at para 74
see also Reasonable Apprehension of Bias
R v Toutissani, ibid. at para 9
R v Karim, 2010 ABCA 401 (CanLII) at para 27 - a mistrial should be allowed only in "the clearest of cases where there is no other way to save the trial"
R v Truscott (1960), 126 CCC 136 (NSCA)(*no CanLII links)
R v Burnett, 2014 MBQB 23 (CanLII) at para 19
- R v Grant (I.M.), 2009 MBCA 9 (CanLII) at para 69
- Grant, ibid. at para 69
- R v T(LA) 1993 CanLII 3382 (ON CA),  O.J. No. 1605, 84 CCC (3d) 90 (Ont. C.A.) at para 8
- Toutissani, supra
- R v Lee, 2002 CanLII 8304 (ON CA)
R v Davis, 2012 ONSC 5526 (CanLII) at para 14, per Baltman J
R v Brace, 2010 ONCA 689 (CanLII), at para 15
see also Right to a Trial Within a Reasonable Time
Circumstances for a Mistrial
A mistrial may be ordered where:
- an opening address and cross-examiination refers to a confession that is later determined inadmissible.
- R v Lizotte,  61 CCC (2d) 423 (Que. C.A.)(*no CanLII links)