Toffoli was a restricted free agent after getting 16 goals and 18 assists in 63 games with the Kings last season. He had postseason surgery on his left knee after struggling with injuries for half of the season, according to his agent, Pat Brisson.
Toffoli has been among Los Angeles' most consistent offensive players since cracking the NHL lineup during the 2012-13 season. He had 14 points in 26 playoff games during the Kings' run to the Stanley Cup title in 2014.
Toffoli then scored 49 points during the 2014-15 season and a career-high 58 points during the 2015-16 season, including 31 goals.
New Kings general manager Rob Blake has reached lengthy contract extensions with Toffoli and frequent linemate Tanner Pearson during the offseason, keeping together his young core despite several huge contracts on Los Angeles' payroll. Pearson agreed last month to a four-year, $15 million extension.
Toffoli's deal has an average annual value of $4.6 million, which will leave the Kings with room under the salary cap to make additional moves. The three-year length of the deal will allow Toffoli to become a free agent again in 2020, when he should still be in his prime at age 28.
The Associated Press contributed to this report.