Known as a centrist on Canada's highest court, his reasoning as a provincial appellate judge in R v Marshall; R v Bernard was adopted by unanimous decision in the landmark Aboriginal title case of Tsilhqot'in Nation v British Columbia in 2014 during his tenure.

[3] When announcing the nomination to the Supreme Court of Canada, Harper stated that Cromwell would not be appointed to the bench until he had answered questions from an ad hoc all-party committee of the House of Commons.

[6] However, this process was bypassed when Cromwell was officially appointed; Prime Minister Harper had expressed concern that waiting for the committee to meet would hobble the court in executing "its vital constitutional mandate effectively.

The decision that drew in large part from his previously rejected Nova Scotia Court of Appeal ruling in R v Marshall; R v Bernard, vindicating his earlier judgement.

[11] On February 12, 2019, former Minister of Justice and Attorney General of Canada Jody Wilson-Raybould retained Cromwell to advise her in the wake of her resignation from the federal cabinet.

[12] In December 2020, Cromwell was commissioned by the University of Toronto Faculty of Law to conduct an impartial investigation of the search process it had used to hire a new director for its International Human Rights Program.