Cardenas was born Stephen Antonio Cardenas on May 29, 1974 in Hampton, Virginia, at the Langley Air Force Base. Spending his early childhood as a military brat, Cardenas was raised in San Antonio, Texas. He is of Puerto Rican and Spanish ancestry. He started training in martial arts when he was about 12 years old and reached black belt in Taekwondo at age 16. Steve Cardenas has been in martial arts for 28 years. He earned 5th degree black belt in Taekwondo and a black belt in Brazilian jiu-jitsu.
At age 20, Cardenas left his native Texas and settled in Los Angeles to audition for a Mighty Morphin Power Rangers role that would change his life. His character, Rocky DeSantos, replaced Jason Lee Scott as the Red Ranger in the Mighty Morphin Power Rangers TV series, and later became the Blue Zeo Ranger for Power Rangers Zeo. He had no previous acting experience and had to learn on the job. Cardenas left the Power Rangers series and retired from acting during Power Rangers Turbo, due to contract disagreements, and possibly to focus on his martial arts career. Many years later, starting at the 2007 Power Morphicon convention, he began making convention appearances with other former cast members.
After Power Rangers, he owns a martial arts studio in Burbank, California and one in his hometown of San Antonio. In 2009, he started a kids-specific program at Hollywood Brazilian jiu-jitsu studio in West Hollywood, and in 2011 he opened the Force/Balance Brazilian jiu-jitsu & Yoga school. Cardenas had become interested in Brazilian jiu-jitsu after losing a friendly match against "a blue belt in BJJ... [he] choked me out in 10 seconds! He was only training for a year and a half at that time and I had been training for 10 yrs. It was an immediate eye opener." The style was more difficult for him to learn than other martial arts disciplines.