Until September 2008 he was playing with the Triple-A Tacoma Rainiers.
On September 5, 2008, he collected his first major league hit, a double, against pitcher Andy Pettitte of the New York Yankees while playing for the Seattle Mariners.
He finished the 2008 season batting .281 with Tacoma and .159 with the Mariners.

He made the 2009 Opening Day roster for the Mariners.
On July 4, 2009 Tuiasosopo made his first rehab start with the AZL Mariners.
Tuiasosopo was activated soon after the All-Star break.
Tuiasosopo hit two home runs against the Portland Beavers on August 28 helping the Rainiers to their seventh straight victory.
He finished the season batting .261 with 11 home runs and 35 RBIs in 59 games for the Rainiers.
In four playoff games, he batted .313 with one home run and four RBIs.

On September 13 Tuiasosopo was called up to Seattle after the Rainiers lost in the first round of the playoffs to the Sacramento River Cats.
He said this about the playoff experience:
We all knew that if we were in the running, all of us would be here in the playoffs, because we know how important that it was, The organization thinks it's important winning in the Minor Leagues, so we knew that we were going to be around and we just wanted to keep winning.
We wanted to see if we could get that ring.
That was important to all of us in that room there.

— Matt Tuiasosopo, mariners.com: September 15, 2009.

On September 27, during the pre-game show on 710 ESPN Radio, color man Mike Blowers predicted that Tuiasosopo would hit his first major league home run in his second at bat of the game on a 3–1 fastball into the left center field second level of Rogers Centre.
Sure enough, in the fifth inning of their game against the Toronto Blue Jays, Tuiasosopo delivered, although the home run went above the left field bullpen on technically what is the first level of the stadium.

Tuiasosopo played in 50 games in the major leagues with the Seattle Mariners during the 2010 season.
He played his first major league games at shortstop, first base, and in the outfield.

Tuiasosopo spent the 2011 season with the Triple-A Tacoma Rainiers.
Tuiasosopo signed a minor league contract with the New York Mets on January 27, 2012, and spent the season with the Triple-A Buffalo Bisons.
Tuiasosopo signed a minor league contract with the Detroit Tigers on December 6, 2012.
 
On March 26, 2013, citing an impressive spring that saw Tuiasosopo hit .327 with four home runs and 10 RBIs, Tigers manager Jim Leyland announced that Tuiasosopo had made the major league team.
After a good start to the season, Tuiasosopo landed on the 15-day disabled list (DL) on June 21.
He returned from the DL on July 5.
On the season, Matt appeared in 81 games for the Tigers, hitting .244 with 7 home runs and 30 RBIs.
Until September 2008 he was playing with the Triple-A Tacoma Rainiers. On September 5, 2008, he collected his first major league hit, a double, against pitcher Andy Pettitte of the New York Yankees while playing for the Seattle Mariners. He finished the 2008 season batting .281 with Tacoma and .159 with the Mariners.
He made the 2009 Opening Day roster for the Mariners. On July 4, 2009 Tuiasosopo made his first rehab start with the AZL Mariners. Tuiasosopo was activated soon after the All-Star break. Tuiasosopo hit two home runs against the Portland Beavers on August 28 helping the Rainiers to their seventh straight victory. He finished the season batting .261 with 11 home runs and 35 RBIs in 59 games for the Rainiers. In four playoff games, he batted .313 with one home run and four RBIs.
On September 13 Tuiasosopo was called up to Seattle after the Rainiers lost in the first round of the playoffs to the Sacramento River Cats. He said this about the playoff experience:
We all knew that if we were in the running, all of us would be here in the playoffs, because we know how important that it was, The organization thinks it's important winning in the Minor Leagues, so we knew that we were going to be around and we just wanted to keep winning. We wanted to see if we could get that ring. That was important to all of us in that room there.
— Matt Tuiasosopo, mariners.com: September 15, 2009.
On September 27, during the pre-game show on 710 ESPN Radio, color man Mike Blowers predicted that Tuiasosopo would hit his first major league home run in his second at bat of the game on a 3–1 fastball into the left center field second level of Rogers Centre. Sure enough, in the fifth inning of their game against the Toronto Blue Jays, Tuiasosopo delivered, although the home run went above the left field bullpen on technically what is the first level of the stadium.
Tuiasosopo played in 50 games in the major leagues with the Seattle Mariners during the 2010 season. He played his first major league games at shortstop, first base, and in the outfield.
Tuiasosopo spent the 2011 season with the Triple-A Tacoma Rainiers. Tuiasosopo signed a minor league contract with the New York Mets on January 27, 2012, and spent the season with the Triple-A Buffalo Bisons. Tuiasosopo signed a minor league contract with the Detroit Tigers on December 6, 2012.  
On March 26, 2013, citing an impressive spring that saw Tuiasosopo hit .327 with four home runs and 10 RBIs, Tigers manager Jim Leyland announced that Tuiasosopo had made the major league team. After a good start to the season, Tuiasosopo landed on the 15-day disabled list (DL) on June 21. He returned from the DL on July 5. On the season, Matt appeared in 81 games for the Tigers, hitting .244 with 7 home runs and 30 RBIs.
Matt Tuiasosopo