On December 20, 2018, Switchfoot announced that Fontamillas had cancer and nine days later they stated that a tumor has been removed and it had not spread or attached to any organs.

He married his wife Kristi, who is a photographer, in December 2005. The couple have two sons, Parker Lennon (born in January 2010) and Jackson (born on October 2, 2013).

In 2002, Jyro and Fontamillas released a Mortal reunion album, Nu-En-Jin.

In 2000, Fontamillas quit his day job and started touring with Switchfoot shortly before the release of their third album, Learning to Breathe. He became an official member of the band in 2003. His first release with Switchfoot was their 2003 break-through album The Beautiful Letdown.

In 1988, Fontamillas, Jyro Xhan, Ray Tongpo and Wilson Peralta released a six-song demo tape, titled Wish Fifteen, on Blue Genius Music as Mortal Wish. Four years later, they signed with Intense Records and changed their name to Mortal. Fontamillas would continue to play with Mortal until 1996 and played in Fold Zandura, also with Xhan, between 1995 and 1999.

In 1985, Fontamillas graduated from Monterey Bay Academy in Watsonville, California.

Jerome Fontamillas (born June 20, 1967) is an American musician. Fontamillas has played in several bands, notably with industrial rock band Mortal and alternative rock band Fold Zandura, with longtime musical partner Jyro Xhan. Since 2003, he has played the keyboards, the guitar and other instruments, as well as sung backing vocals in Switchfoot, with which he has released eight studio albums.

Fontamillas was born on June 20, 1967 in Pasay City in the Philippines. When he was three years old, his family moved to the United States, where they lived in Chicago and then California. He started taking piano lessons when he was a child.