His father was a fisherman in the southern village of Mangagoy, Surigao Del Sur, but a typhoon claimed his life in a boating accident when Dennis was just 5 years old.

At 9 years of age, Orcollo dropped out of school because of financial problems and to focus on billiards and run racks on his grandfather's pool table, routinely beating grown men for 20 pesos a game.

At 16, despite pleas from his mother and grandfather, who wished he'd stay and become a fisherman, Orcollo left home for a gold mining town called Compostela, where he hustled pool.

Four months later, Orcollo ruled the inaugural Qatar World Nine-ball Open tournament defeating Niels "The Terminator" Feijen of Netherlands 13–5 in the championship match to bag the title and the top purse of $40,000.

In 2013, Dennis Orcollo and Lee Vann Corteza clinched the World Cup of Pool after defeating the Dutch tandem of Niels Feijen and Nick van den Berg, 10–8, at York Hall in London, England.

They became the third Filipino duo to win the annual single-elimination tournament for doubles teams in nine-ball competition after Efren "Bata" Reyes and Francisco "Django" Bustamante won the inaugural event in 2006 and then repeated in 2009.

Orcollo sought redemption after he came up close in 2010 World cup of Pool with a second place finish with his partner Roberto Gomez, bowing to eventual winners Li He-wen and Fu Jian-bo of China.

[25] In 2016, Orcollo defeated Shane Van Boening, 200–121 to win the U.S. Open Straight Pool Championship,[26] a tournament that has not been held previously for sixteen years.

[27] In 2020, Orcollo recorded a 120–119 victory against Shane Van Boening to be crowned The Money Game King in a three-day one-on-one 9-ball tournament held at Bill's Bar and Billiards in Oklahoma City.

[31] In 2022, Orcollo was the fourth Filipino pool player to be inducted into the BCA Hall of fame, joining fellow countrymen Efren Reyes, Francisco Bustamante, and Jose Parica.