He previously served as the team manager for the NLEX Road Warriors of the Philippine Basketball Association (PBA).

[3] Larry first played for the Ateneo de Manila High School Blue Eaglets in the University Athletic Association of the Philippines Juniors Basketball division, leading them to numerous winning seasons and championships along with Enrico Villanueva, Wesley Gonzales, BJ Manalo, and Bajjie del Rosario.

They defeated Far Eastern University Tamaraws 67–63 then faced the De La Salle Green Archers in the best-of-3 finals.

During the summer, the Ateneo-Hapee team joined the commercial and amateur Philippine Basketball League and won the championship under coach Joel Banal.

[7] At the start of the 65th season of the UAAP, with a championship caliber coach in Banal, the Ateneo de Manila community had very high hopes of finally ending the 14-year drought.

[9] Furthermore, they spoiled the De La Salle Green Archers chances of sweeping the 14 game eliminations, which would have given them an outright berth in the championship round.

[10] The team won both games and faced the De La Salle Green Archers in the finals in a best of 3 series.

[16] He missed their next game (which was against the NU Bulldogs) due to a fractured nose bridge he sustained in team practice, and Ateneo lost.

[18] He suffered an ACL injury on his left knee while driving to the basket in the fourth game against UP that ended his UAAP career.

[20] Before entering the PBA, Fonacier continued to rehab from his ACL injury, and took master's classes in communications.

[22] In the next conference, the Philippine Cup, he helped Red Bull reach the finals, where they lost to the Purefoods Chunkee Giants in six games.

[24] This made him the lowest picked player in PBA history to win the award, until Aaron Black broke the record.

In a 92–89 loss to the Air21 Express during the 2006–07 season, Fonacier had a chance to make a game-winning play, but his pass was stolen by Yancy de Ocampo.

There, he split time with Lordy Tugade, Chris Calaguio, and former Ateneo teammate Wesley Gonzales on a team that was in "win-now" mode.

[28][1] After some games with Magnolia, he was then dealt to the Alaska Aces with his teammate LA Tenorio in exchange for Ken Bono and Mike Cortez.

He had to master Coach Tim Cone's triangle offense and come off the bench, which took some time to adjust for him.

[22][1] In a win over the Coca-Cola Tigers during the 2008–09 Philippine Cup, Fonacier scored 13 points with three three-point shots.

[39] In the Game 1 of their Philippine Cup semis against Petron, Fonacier scored half of his 22 points in the fourth quarter, and made two clutch free throws to secure the win.

[58] In a close Commissioner's Cup game against NLEX in which they were up by one with eight seconds remaining, he called a timeout even though the team didn't have one.

[61] During the offseason, Fonacier re-signed a three-year deal to stay with Talk 'N Text for three more years.

[67] In a win over Globalport, he had 14 points and a crucial offensive rebound that allowed Ranidel de Ocampo to make the game-winning shot for TNT.

[73] With a new head coach in Nash Racela, he enjoyed a career resurgence as in their first five games of the conference, he averaged 10.8 points built around 2.2 triples, three rebounds, 1.4 assists, and 0.8 steal in 27.3 minutes.

[85] NLEX then clinched a spot in the quarterfinals with a 103–100 win over SMB as he logged 16 points, four rebounds, three assists, two blocks, and one steal in 29 minutes.

[92] NLEX lost three more games after that, but they were able to stop the losing streak with a win over Ginebra in which he produced 17 points on 7-of-12 shooting.

[93] Then he contributed 17 points, six rebounds, and one block while also going 4-of-4 from three as Kiefer Ravena made the game-winning jumper over the Bolts.

[96] In the 2018 Commissioner's Cup, Fonacier had an all-around performance of 12 points, seven boards, and six assists in a win over the Columbian Dyip.

[99] He was then ruled out for the rest of the Commissioner's Cup after a collision in mid-air with Ginebra's Jervy Cruz led to a bruised rib and a collapsed lung.

[24] In his final conference, he played in seven games and averaged 1.2 points as the Road Warriors didn't make the playoffs.

[121] The following year, Fonacier begged off from the national pool, as he had been playing through multiple back and foot injuries and needed to rehab.

[1][136] He isn't active on social media, but has spoken up on political issues, such as when he posted his thoughts about the Anti-Terrorism Bill.