Melancon graduated from Golden High School in Colorado where he played baseball, basketball, and football. He was then drafted by the Los Angeles Dodgers, but chose to attend the University of Arizona.
Despite appearing in only 32 games in his first season with the San Francisco Giants in 2017 due to a forearm injury, Mark has recorded 179 career saves in the last seven seasons (2011-17). He reached a personal best with a major league-leading – and club record – 51 saves in 2015 with the Pittsburgh Pirates. He converted 51 of his 53 save chances in ‘15 for an MLB-best 96.2 save percentage and was the recipient of the Trevor Hoffman National League Reliever-of-the-Year award. A three-time National-League All-Star with the Pirates, Mark was traded to the Washington Nationals on July 30, 2016 and went 17-for-18 in save opportunities for the Nats en route to the N. L. East title. His 47 combined saves in ’16 were tied for second most in the majors. Mark signed a four-year contract with the Giants as a free agent on December 5, 2016.
He has a shark named after him from a trip taken to Southern New Zealand in which a diver tagged one of the sharks with the name “Melancon” in his honor.