He will earn $4.5 million the first year and $2.5 million the second, following the pattern of front-loading free agents’ contracts in case of a lockout after the 2011-12 season.
Gagne, 31, scored 17 goals and 40 points and was -12 defensively in 63 games with the Tampa Bay Lightning last season. Before that, he played 10 seasons for the Philadelphia Flyers, peaking at 47 goals and 79 points in the 2005-06 season.
One of his Philadelphia teammates was Mike Richards, who was acquired by the Kings last week.
Gagne joins an already large Flyers alumni club in Los Angeles, with Coach Terry Murray, assistant John Stevens, General Manager Dean Lombardi and winger Justin Williams having Philadelphia on their respective resumes.