Led by Brewin, the "Japanese Canadian Reference Case" was heard by the Supreme Court of Canada and later, on appeal, by the Judicial Committee of the Privy Council.

Brewin was also retained by a committee of Japanese Canadians who had been detained during the Second World War as "enemy aliens" in order to try to have their property restored.

Brewin stood as a CCF candidate several times, starting with the 1945 Canadian federal election in the riding of St. Paul's, but was unsuccessful.

[3] Coming from the theological tradition of figures such as Richard Hooker, F. D. Maurice, and William Temple,[7] Andrew Brewin considered himself a Christian socialist and wrote a number of books and pamphlets on the topic.

[9] Andrew Brewin wrote the book Stand on Guard: The Search for a Canadian Defence Policy, published by McClelland & Stewart in 1965,[3][10] that explored Canada's military's changing role in the mid-twentieth century, including its participation in the then new concept of United Nations peacekeeping.