[2][3] In 2009, he led his school to the NOPSSCEA finals where he scored 37 points but lost to St. John's Institute (SJI).

He then transferred to SJI, where in his first year, he scored 45 points in the NOPSSCEA finals, but lost to the West Negros University Junior Mustangs.

[5] In 2009, Montalbo was part of a Western Visayas selection that won the silver medal in that year's Palarong Pambansa.

[8] The entire DLSU coaching staff, star player Jeron Teng and even chief Archers patron Eduardo ‘Danding’ Cojuangco made a trip to his hometown of Bacolod just to recruit him.

That season, the De La Salle Green Archers won the championship over the UST Growling Tigers.

[14] In 2014, Montalbo and Subido participated in the Nike All-Asia Basketball Camp, where they both made the Top 20 Asian Players list.

[20] In 2015, during a Filoil Flying V Preseason Cup match against the UE Red Warriors, Montalbo suffered an ACL injury.

[22] He used the time away from basketball to recover and focus on his studies, making the dean's list for his course in business management.

That performance led to him earning a Player of the Week award, becoming the third Archer that season to win one after Ben Mbala and Teng.

[25] Later in the tournament, he hit a clutch triple against Adamson that gave La Salle their eighth straight win.

[27] In their last game of the elimination round, he scored 13 points in a win over FEU, and the Archers finished first in the standings with a record of 13–1.

[37] He then scored 12 points in a win over the UP Fighting Maroons that secured La Salle into second place.

[41] He rallied the Archers in Game 2 while contributing nine points, five assists and three steals, and they tied the series.

[50] Later that year, he also joined the Makati Super Crunch in the Maharlika Pilipinas Basketball League (MPBL).

[55] In a 2021 Philippine Cup loss to the San Miguel Beermen, Montalbo led TNT with 13 points.

[56] That performance led to him starting the following game, and he had 13 points, three rebounds, and two steals in a win over the NLEX Road Warriors.

[67] In Game 4 of the Governors' Cup finals against Ginebra, he scored a season-high 16 points by making four treys as the team made a finals-record 21 three pointers and tied the series.

[70] As of the end of 2023–24 season[71] In 2022, Montalbo made his Philippine national team debut in a win over India, in which he had eight points.

[73] As a TNT player for Coach Chot Reyes, he received ire from Gilas fans for being on the roster over the likes of CJ Perez.