Jarvis was born in New Jersey, United States to an Armenian-American mother and English father. As a child, he moved to Devon, United Kingdom with his family. In his own words he has stated that he feels no affiliation with New Jersey except that "Kevin Smith was born there and I love his work". Jarvis first started writing, recording music, and creating his first films on VHS when he was twelve. At age 16 he left education at Eggbuckland Community College to pursue a career in music and film instead of choosing to attend a sixth form, and at 19 he released his self-titled debut album.
Jarvis confirmed his second album's title as Is the World Strange or Am I Strange? on his official Facebook page. The first single released from the album is "Gay Pirates", which was released on 23 January 2011. The single's music video, which was directed by Cosmo, was a viral hit and was popular among celebrity tweeters such as Stephen Fry and John Barrowman. The song was featured as Record of the Day and AOL's Spinner video of the day. "Gay Pirates" was voted number 85 on the Triple J Hottest 100 of 2011, which aired on Australia Day in 2012. The album itself was given an 8.5/10 rating from Soundblab album reviews. He announced in an interview with TNC that he had begun work on his first feature film, called The Naughty Room. The film premièred on BBC Four on the 20/08/12, shortly after the release of Jarvis' third studio album, titled Think Bigger. Cosmo toured the UK in late 2012 supporting Mad Dog Mcrea, for whom he penned the song "Waiting on the Hill". The comedy film Hawk(e): The Movie (2013) features several songs by Cosmo Jarvis. In January 2013, "Love This" came in at number 59 on the Triple J Hottest 100, 2012.