He was a puisne justice on the Supreme Court of Canada from his 2011 appointment by former Prime Minister Stephen Harper until his retirement in 2022.
[5] However, Moldaver's plans changed with the opportunity to finish the last six months of his articles with a leading criminal defence lawyer, Goldwyn Arthur Martin.
[5] In addition, he also admired the television show Perry Mason, which was based on a fictional charismatic criminal defence lawyer.
Moldaver stated that the thought of "being able to defend a person charged with murder, who was innocent, and have the real culprit confess after a blistering cross-examination was too much for [him] to resist".
[6] He had the opportunity to work with Justice Marc Rosenberg, and notable lawyers Eddie Greenspan and Alan Gold.
[19] In 2007, Moldaver joined the court in acquitting Truscott of his 1959 rape and murder convictions, due to new medical evidence and fresh testimony.
[16][23] Moldaver ultimately decided to overturn the conviction due to the Crown's failure to disclose a key piece of evidence.
[25] In 2011, Moldaver, along with a unanimous court, sentenced Momin Khawaja to life in prison for engaging in terrorist activity.
[26][27][28] The Court held that harsh sentences are required to deter individuals from engaging in future terrorist activity.
[29][30][31] His nomination and eventual appointment filled one of the two vacancies left by retiring Justices Ian Binnie and Louise Charron.
Moldaver's nomination raised some concern, due to his prior statements made about criminal defence lawyers and the Charter.
By and large the governing principles are firmly established.These comments received pushback from criminal lawyers, who accused Moldaver of interpreting the Charter as a "weed to be stunted" instead of a "vital living tree".
[39][40] In expressing his disapproval with counsel who clog the justice system by bringing baseless Charter claims, he suggested he wants to see changes that will "simplify the criminal law, and in the process, restore the public's faith and confidence in our criminal justice system".
[36] He has questioned whether they overcharge, refuse to yield to reasonable defence requests, and push the evidentiary envelope beyond what is needed for a conviction.
[41][42][34] Both the Bloc Quebecois and the New Democratic Party expressed their concerns over his lack of French proficiency and claimed they would not support his nomination.
[41] The Quebec Bar Association expressed concerns his appointment would deny Francophones equality before the law and was a step backwards because his predecessor – Justice Louise Charron – was bilingual.
[41] Moldaver expressed his respect for the French language and apologized for his inability to speak it; he committed himself to becoming more proficient in the future.
[44] In 2014, writing for the majority in R v Hart, Moldaver redefined the common law test for the admissibility of confessions obtained through a Mr. Big sting operation.
[47] He argued that the Court should have shown judicial restraint and upheld Parliament's three-year mandatory minimum sentence for illegal possession of a loaded firearm.
[57][58] Police pulled MacKenzie over during a highway traffic stop and, through the use of a sniffer-dog, discovered a large amount of marijuana.
[59][57] MacKenzie alleged the dog's sniff violated his section 8 Charter rights against unreasonable search and seizure because the police lacked reasonable suspicion he was involved in a drug related offence.
[46][63] He held that "misconduct that offends the community’s sense of fair play and decency will amount to an abuse of process and warrant the exclusion of the statement.
[47][65][66] Writing for a 6–3 majority, Chief Justice McLachlin stated that criminal punishments need to reflect the seriousness of the crime.
[47][65][66] He argued that the illegal firearm possession provisions are hybrid offences and therefore only carry the mandatory minimum sentence if the Crown proceeds by indictment, instead of by summary conviction.
[69] He stated that the nature of the hybrid offence acts a "safety valve", which ensures that the least serious offenders will not face three years in prison.
[5] Moldaver has volunteered as a guest judge on final panels for various national law school moot competitions.