With a lifelong interest in the Canadian Forces, he became an officer cadet and rose to the rank of lieutenant-colonel.
After winning re-election again in 1978 and in 1982, he became the Minister of Natural Resources, Government House Leader, and Deputy Premier.
Gerald Merrithew resigned his provincial seat to run as a Progressive Conservative Party of Canada candidate for the Saint John riding in the 1984 Canadian federal election.
He and his wife retired to their farm in Springfield, New Brunswick at the head of the Belleisle Bay.
[citation needed] Active with numerous Military and Veterans Associations, Merrithew was a member of the Queen's Privy Council for Canada and also held several directorships including the "26th Battalion Overseas Association Inc." where in 1995 he was instrumental in publishing the history of the Battalion by S. Douglas MacGowan (ISBN 1896270026).