He grew up in Michigan before moving to Fremont, California where he played junior hockey for the Santa Clara Blackhawks and San Jose Jr.

On November 24, Martinez scored his first NHL goal, on the power play, in 4–1 loss to the Montreal Canadiens at the Bell Centre against goaltender Carey Price.

[4] Martinez had his first multi-point game December 4, 2010, including a goal against Chris Osgood of the Detroit Red Wings in a 3–2 victory for the Kings.

He scored two series winners en route to the Kings' second Stanley Cup title – on June 1, 2014, Martinez scored 5:47 into overtime of Game 7 of the Western Conference Finals against the Chicago Blackhawks on goaltender Corey Crawford; 12 days later, in Game 5 of the 2014 Stanley Cup Finals against the New York Rangers, a shot by Tyler Toffoli, which rebounded off goaltender Henrik Lundqvist in double overtime, led to another Martinez goal.

After hoisting the Cup himself, he handed it to former Kings teammate Jonathan Quick, who had joined the Golden Knights earlier in the year.

"[10] Leaving the Golden Knights as a free agent, Martinez signed a one-year, $4 million contract with the Chicago Blackhawks on July 1, 2024.

[11] Martinez represented the United States at the 2018 IIHF World Championship where he recorded one goal and two assists in ten games and won a bronze medal.