Slater played college football for the UCLA Bruins, where he earned first-team All-Pac-10 honors, and was selected by the Patriots in the fifth round of the 2008 NFL draft.

Slater lettered in football for two seasons at Servite High School in Anaheim, California, where he was teammates with Ryan Kalil.

He was selected as the 2003 Orange County Register Boys Track and Field Athlete of the Year as a senior.

[4] Slater attended the University of California, Los Angeles and majored in political science and history, while playing for the Bruins football team.

He also returned 34 kicks for a 29-yard average and 3 touchdowns which tied the lead in the nation and set the UCLA record.

[11] Matthew's father, Jackie Slater, was pleased with the selection and told the Boston Herald that he received phone calls from "scouts, administrators in the NFL who knew me and my son, and they said, ‘Jackie, this could not be a better fit for your son to start being a pro football player.

Slater played in 14 games in his rookie 2008 season, returning 11 kickoffs for 155 yards and recording 12 tackles on special teams.

He also played in a reserve role at wide receiver and on special teams coverage units in the postseason game against the Baltimore Ravens.

In his defensive start against the Indianapolis Colts, Slater forced a fumble and finished the game with a team-high six tackles.

[21][22][23][24] At the time, the Slaters were one of five active father-son families selected to at least one Pro Bowl apiece.

[26] Slater, who became a free agent after the 2011 season, signed a three-year contract to return to the Patriots in 2012.

[28][29] Slater was also named to the Pro Bowl and the 2012 PFW/PFWA All-Pro for the lone AFC special teamer position for the second straight season.

[30][31] In his sixth season with the Patriots, Slater continued to be a reliable captain and inspirational leader on and off the field.

[33] On November 26, 2014, it was reported that Slater signed a two-year contract extension to remain with the Patriots through the 2016 season.

On January 4, 2017, Slater was announced as the winner of the Bart Starr Award, given annually to a player who exemplifies character and leadership on and off the field.

[41] Slater had a role as special teams captain and successfully called the coin toss before overtime began.

[47] During a Week 4 16–10 road victory over the Buffalo Bills, Slater scored his first and only NFL touchdown on an 11-yard blocked punt return.

[51] With quarterback Tom Brady's departure and the release of placekicker Stephen Gostkowski, Slater became the longest active member of the Patriots.

[54][55] Slater made his tenth Pro Bowl and was a Second-team All-Pro selection for the third time in his career.

[62] During the 2024 off-season, Slater was hired by the New England Patriots new head coach Jerod Mayo to be on his staff in a "right-hand man" capacity.

[64] Slater was not retained after Mayo's firing and the hiring of new head coach Mike Vrabel.

[70][71] On October 25, 2016, Slater hosted a "pop-up" fundraiser to benefit Hurricane Matthew victims.

[72] He raised over $60,000 for Samaritan's Purse to assist in their efforts in the Carolinas and Haiti after the devastating hurricane barreled through those regions.