Portacio was born in Sangley Point, Cavite City, Philippines. He grew up in places such as Midway Island and New Mexico before his family settled in San Diego, California. He began reading comic books at the age of ten, when his neighbor decided to get rid of her husband’s collection, and through this, he discovered the work of creators such as Jack Kirby and Neal Adams, who were the two most important influences on Portacio’s art. Though Portacio dreamed of becoming an astronaut, his height and eyesight did not meet the necessary requirements, which determined that art would be his vocation. In high school, he continued to create his own comic books with his longtime friend, Scott Williams, who would one day be a prolific comic book inker in the industry.
Portacio attended his first comic book convention in San Diego, where Marvel Comics editor Carl Potts, after seeing Portacio’s portfolio, offered him the job inking over Frank Cirocco and Chris Warner’s pencils on the 1984 series Alien Legion. The following year, he inked over Art Adams’ pencils on the 1985 miniseries Longshot.
Later he was given assignments as a penciller as well. Portacio became noted for his work on such titles as The Punisher, X-Factor, and The Uncanny X-Men, for which he co-created the character Bishop with John Byrne and Jim Lee.
In 1992, Portacio left Marvel to co-found Image Comics with six other high-profile artists. He quickly withdrew from Image due to his sister’s illness. He eventually published his title Wetworks through Jim Lee’s Wildstorm imprint in 1994. Other notable series that Portacio worked on include Stone and Marvel’s controversial Heroes Reborn storyline within Iron Man.
Stan Lee interviewed Portacio in the documentary series The Comic Book Greats.
In August 2000, Portacio fell into a diabetic coma as a result of a failing pancreas. He woke up a week later, thirty pounds lighter, and unable to walk, stand or even draw. Only six months later was he able to pick up a pencil and draw. According to his blog, “My mind could see what I wanted to draw but my hand couldn’t accomplish it.”
In 2006, Portacio returned to his artistic duties at Wildstorm on Wetworks vol. 2, which was being written by Mike Carey. Portacio left the book with issue #6. He also began art duties on the monthly DC Comics series Batman Confidential.
On June 9, 2008, it was announced that Portacio would be the new artist on Spawn starting in October 2008 with issue #185, providing pencils with Spawn creator Todd McFarlane returning as co-writer with Brian Holguin as the new creative team.
Following his run on Spawn he has done more work with Marvel. He contributed pencils to Hulk #18 in 2008, and will be contributing pencils to an upcoming issue of The Uncanny X-Men.