At age 5, his mother decided to move back to Freetown, Sierra Leone, where he spent the next 14 years living between the fruit farm of his great, great uncle, Sir Henry Josiah Lightfoot Boston, the first indigenously elected Governor-General of Sierra Leone [1] and with his mother's family in The Gambia and Zimbabwe.

Numerous tours round the world with the group and their work with many of the world's biggest recording artists led to opportunities for Macarthy to carve a career as a session singer, providing studio/live backing vocals for artists and groups such as Blur, Madonna, Beautiful South, Spiritualized, Death in Vegas, Billie Piper, Westlife, Will Young, P Diddy, Atomic Kitten, Mariah Carey, Celine Dion, Paul Carrack, Elton John, Art Garfunkel, Boy George, Eternal, Manu Dibango, R. Kelly, Jessye Norman, Gloria Gaynor, Mica Paris, Paul McCartney, Erasure, Andrea Bocelli, Heather Smalls, Van Morrison and Tom Jones.

[4] The school found out about his singing background after he'd completed his first year of study and tried to pressure him to transfer to their Musical Theatre course, but Macarthy refused.

His first movie appearance was in Danny Boyle's 2004 feature Millions,[5] in which he played the Ugandan martyr Gonzaga, followed by appearances in A Touch of Frost, Doctors, EastEnders, Torchwood and the Anthony Horowitz mini-series Collision; he also played the male lead in the supernatural thriller Patient 17, which went on to win the London Independent Film Festival award for Best Sci-Fi/Horror Feature in 2012.

In August 2022, Variety announced Macarthy would be joining Peacock’s new TV adaptation of Vampire Academy by Julie Plec and Marguerite McIntyre as a recurring guest star.