In the late 1970s, Duffy became known for his outspoken support of Northern Irish independence,[6] although he did concede that there would need to be some form of federal structure covering the entire island.[7] He objected to the arrangements for the 1982 Northern Ireland Assembly election, refused to stand, and unsuccessfully attempted to persuade the SDLP to boycott the election,[8] and called for its assembly members to withdraw after Seamus Mallon was disqualified.[9] Following this, he withdrew from involvement in the SDLP, although he was re-elected as a nominal party member to Cookstown District Council in 1985 and 1989.[3][10]
Outside politics, Duffy built up a large legal practice, with offices in small towns across Northern Ireland. He was also active in the credit union and co-operative movements. At the time of his death in 1996, he was a member of the board of the International Fund for Ireland.[11]
He died on 19 August 1995, and was survived by his wife Mary and their three sons.[1]