Isaac Mercer (September 3, 1912 – 2002) was a lawyer and politician in Newfoundland. He represented Port de Grave from 1951 to 1956 and Fogo from 1956 to 1961 in the Newfoundland House of Assembly.
He was first elected to the Newfoundland assembly in 1951. After leaving politics in 1961, Mercer continued to practice law until 1977. In 1989, he was named an honorary life member of the Canadian Bar Association. He died in 2002.