Oliver Mowat Biggar, CMG, KC (October 11, 1876 – September 4, 1948) was a Canadian lawyer and civil servant. He was the second judge advocate general for the Canadian Militia and the first chief electoral officer of Canada. He also served as the first Canadian co-chair of the Canada–United States Permanent Joint Board on Defense. Biggar was well known as a leading Canadian lawyer with expertise in public law and patent law.