Theodore Roosevelt O'Neil Meighen (October 1905 – 1979) was a Canadian lawyer and philanthropist.
He was the eldest son of former Prime Minister Arthur Meighen and Isabel Cox.
He attended the Royal Military College of Canada in Kingston, Ontario in 1925, student #1865.
He practiced law in Montreal, and became a senior partner in the firm of McMaster Meighen.
During World War II, he was based in Halifax, Nova Scotia while serving in the Royal Canadian Artillery.