Merrithew graduated from the New Brunswick Teachers' College, then obtained his B.A. & B.Ed. degrees from the University of New Brunswick. With a lifelong interest in the military, he became an Officer Cadet in and rose to the rank of Lieutenant-Colonel. As a High School Principal, he was active not only in the educational field, but military, recreational as well as cultural Affairs that led to his entering politics. First elected to Saint John City Council in 1971 he went into Provincial politics in 1972, winning a by-election for the Provincial Progressive Conservative Party. Re-elected in 1974, he would be appointed to the Cabinet as Minister of Commerce & Development. After winning re-election again in 1978 and in 1982, he became Government House Leader and the Minister of Natural Resources.
Gerald Merrithew resigned his provincial seat to run as a Progressive Conservative Party of Canada member in the 1984 Federal election. Elected to the Canadian House of Commons in Ottawa, and with his party winning the election, Merrithew was immediately appointed Minister of State - Forestry & Mines. After winning his seventh consecutive election in 1988, he was appointed Minister of Veterans Affairs.
In 1993 he resigned from Cabinet and did not seek re-election. Active with numerous Military and Veterans Associations, Gerald Stairs Merrithew is one of the Members of the Queen's Privy Council for Canada and also holds a several directorships including the "26Th Battalion Overseas Association Inc." where in 1995 he was instrumental in publishing the history of the Battalion.