During that time, he served as solicitor for the city of Guelph and Wellington County, as well as Crown prosecutor.

[citation needed] On July 20, 1935, Kerwin was appointed a puisne justice of the Supreme Court of Canada.

[1] In 1954, after 19 years on the court, Kerwin was appointed as Chief Justice, replacing the retired Thibaudeau Rinfret, with the honorific "The Honourable".

[2] Kerwin was deemed to be in poor health when appointed and there were rumours he would retire during his tenure but served 9 years.

[2] Five different puisne judges were appointed to the court during those years, an unusually high number.