The Kings also signed restricted free agents Justin Auger, Andrew Crescenzi, Zachary Leslie, Kurtis MacDermid, Michael Mersch, Jonny Brodzinski and Paul LaDue.
Gravel broke through as an NHL regular last season, scoring seven points in 49 games while getting a steadily increasing role on the power play. He scored his first and only NHL goal Feb. 23 against Boston.
Gravel filed for arbitration earlier this month after receiving a qualifying offer from Los Angeles. He was the Kings' only remaining restricted free agent who logged significant time in the NHL last year.
LaDue's one-year extension is worth $874,125 at the NHL level. The rookie defenseman scored eight points in 22 games last season, and he also logged 38 games in the AHL after helping North Dakota to the 2016 NCAA championship.
Brodzinski, who got a two-year extension, also made his NHL debut last season with two points in six games for Los Angeles. He was a standout scorer for the Kings' AHL affiliate in Ontario.
Auger, Crescenzi, Leslie, MacDermid and Mersch are all regulars in Ontario.