Answer
Jack Lynch succeeded William Cosgrave as Taoiseach, serving from 1966 to 1973 and again from 1977 to 1979. Lynch was a member of Fianna Fáil, the main opposition party during Cosgrave's tenure as Taoiseach. His election marked a shift in Irish politics, as Fianna Fáil had been out of power for 16 years.