On Friday, the Kings announced the deal with Toffoli, who would have become a restricted free agent next month.
Toffoli established career highs with 23 goals, 26 assists, a +25 rating and five short-handed goals last season for the Kings. He was Los Angeles' third-leading scorer and led the NHL in short-handed points and goals.
The former second-round pick has played three NHL seasons, scoring 37 goals. He won a Stanley Cup title with the Kings in 2014.