Born in 1969 in Apia in Samoa, he emigrated to New Zealand aged four and grew up in West Auckland.

Oscar began his career as a reporter with the Auckland Star, Sunday Star, and Independent Radio News before moving to Christchurch in 1990 to work on TVNZ's teenage show Life, while at the same time becoming part of The Performing Arts Trust. He helped establish Pacific Underground (a Christchurch-based theatre group), where his first co-written play Fresh off the Boat was developed. Following this success, Pacific Underground toured a number of critically acclaimed Pacific Island plays to schools around New Zealand and the Pacific. In 1996, A Frigate Bird Sings (co-written with David Fane) gained success at the 1996 New Zealand International Arts Festival; Oscar's first solo venture as a playwright, Dawn Raids, premiered in Auckland in 1997 and in 1998 he was awarded the Bruce Mason Playwriting Award. In 2004, Oscar wrote Niu Sila with Dave Armstrong, which played to sell-out crowds. In 2006 Oscar (and Dave Armstrong) were amongst recipients of the inaugural Arts Foundation of New Zealand Award for Patronage discretionary donation from Denis & Verna Adam.

Oscar is a member of the Naked Samoans comedy group, who performed in the International Laugh Festivals, from 1998 to 2002. He co-hosted TV3's coverage of Super 12 Rugby and the weekly sports show, SPORTZAH as well as being a writer/performer for Skitz and Telly Laughs for TV3. He has been on the Panel for TV3 in a story-liner for Shortland Street and has featured on documentaries about the Otara Markets and Racism in New Zealand in 2001/2002. Oscar is also a presenter on Nui FM's breakfast show.

He currently works with the Naked Samoans on the TV3 series Bro' Town which has won Best Comedy at the 2005, 2006 and 2007 NZ Screen Awards. Bro' Town entered its fifth season in 2008.

He acted and co-wrote the hit film Sione's Wedding which reached the number one position in the New Zealand box office in its first week of release and had the biggest opening weekend of any New Zealand-made film, grossing over $3 million. In 2007 Oscar was one of five high profile New Zealanders who lent their names to Inspire Me, a nationwide advertising TV campaign promoting public libraries, and also toured with the show Naked Samoans Go Home - Again! He featured in the Listener's list of New Zealand's 50 most powerful people at #36, and was appointed as a member of Creative New Zealand's Arts Council for a three-year term.

Early in 2008, Oscar stood in for Kim Hill on the Saturday morning slot on Radio New Zealand National. Oscar and bro'Town colleagues took to the stage during the New Zealand International Arts Festival.

Oscar was a joint recipient (with playwright Dave Armstrong) of an Arts Foundation Award for Patronage discretionary donation from Denis & Verna Adam. He received an Arts Foundation Laureate Award in 2006 and was made a Member of the said Order (M.N.Z.M.) in the 2009 New Year's honours list for his services to television and the theatre.