Ruivivar's early appearances include the films Race the Sun (1996) and a minor character in Starship Troopers (1997). Ruivivar's breakthrough role came in 1999 as Carlos Nieto, a paramedic in the action/drama series Third Watch (1999–2005), which centers around the life of police officers, paramedics, and firemen of a fictional precinct and fire station in New York City. In the show, Carlos was a Hawaiian-born Filipino-American who was abandoned by his family and spent his youth in various foster homes.

Ruivivar was born in Honolulu, Hawaii to a musician father. In January 1998 he married Actress Yvonne Jung, who would later appear in seasons 5 and 6 (2003–2005) of Third Watch as FDNY EMS Paramedic Holly Levine. In the show, Ruivivar and Jung's characters became a couple and got married in the series finale. In real life they have 2 children; son Kainoa was born on (2002-08-28) August 28, 2002 (age 15) and daughter Levi was born on (2006-05-03) May 3, 2006 (age 11).

After Third Watch, Ruivivar remained in the drama genre, usually playing a police officer, detective or FBI agent in various TV series, such as Traveler, Quantico, Numb3rs, Criminal Minds, CSI: Crime Scene Investigation (all 2007), and Lie to Me (2009).

In 2010, he had a main role in ABC's The Whole Truth as Alejo Salazar. He is currently appearing in a recurring role as Alex Longshadow in Banshee and Batman/Bruce Wayne in Beware the Batman.