Magasiva was born in Apia, Samoa, but raised in Wellington, New Zealand, since he was two years old. He was the younger brother of actor Robbie Magasiva. It was Robbie who inspired Magasiva to become an actor, after being signed up with an acting agency and acquiring small roles. In 1999, he made a minor appearance on Shortland Street as Elvis Iosefa, a relative of Louie Iosefa. Then in 2001, he landed a role in a six-part Māori language television series called Aroha. The series went on to screen at the International Film Festival in Auckland, receiving critical praise. Finally in 2003, Magasiva made the leading roles in both Power Rangers: Ninja Storm and Shortland Street. He stayed on Shortland Street until 2006. By then, he played the title character in the comedy filmSione's Wedding, which starred his brother Robbie and other members of the Naked Samoans. In 2007, he appeared in the horror film30 Days of Night. In 2009, Magasiva made guest appearances in Diplomatic Immunity and Outrageous Fortune. In 2011, he returned as Vinnie Kruse on Shortland Street. Outside his work on television and film, Magasiva acted in theatre, including Two Days in Dream in 2003. Another play that he acted in was Sex with Strangers, which was written by Mitchell, though Two Days in Dream was well received by critics. In 2008, he co-starred with brother Robbie in the play Where We Once Belonged. Magasiva also appeared in nine Lift Plus commercials in New Zealand and also took over his brother's role as the Small Blacks TV News presenter opposite Conrad Snakey Smith. In January 2017, he helped pull a man from his burning car.
On 18 December 2019, a name suppression order was lifted, revealing that Pua Magasiva had been convicted of domestic assault against his wife in April, 15 days before his death. Pua was sentenced to 70 hours of community work, and six months of supervision. According to his widow, he had engaged in a regular pattern of abuse, concussed her three times, and threatened to harm her, himself, or their daughter, if she went to the police. She claimed to have later found a diary belonging to him showing "pages... full of haunting images, tortured thoughts and self-loathing" and admitting that he had always been violent and angry. On 11 May 2019, Pua Magasiva died of a suspected suicide in a hotel room in Wellington, New Zealand. His widow stated that he attacked her in a drunken rage the night he died.
