In 2005, he travelled to London to record with a producer named Andy Wright,[1] and played in various venues and festivals throughout England, including the Tavistock Festival on Portobello Road.[citation needed]
In 2006, he played the lead role in Dha Theanga, an Irish program on BBC TV. He also rewrote and arranged the music for the show.[2] Harkin was invited to support John Martyn and David Kitt on their Irish tours and BBC Radio Ulster called him the "Irish Jack Johnson."[3]
Harkin was part of the band Celtic Thunder, which performed in the United States, Canada, and Australia.[4] Celtic Thunder had two #1 selling DVDs and three #1 selling albums on the World Billboard charts.[5][6] Harkin began working with the band in 2007[7] and wrote "Lauren and I" for the band.[8][9]
After nearly ten years with the group, he decided to take time off and tour independently. Harkin has now recorded more original songs including: "How I Wish," "Daisy Fields," "Vanity," "September Sessions," and "All Day Long".
Harkin's self-titled solo album was released in Canada on 4th September 2012 and in the United States on 18th September 2012. The album was released with Verve Records, to which he was signed by Grammy Award-winning producer David Foster.[10] It reached the No. 8 spot in Amazon's Pop Music Charts and the #1 spot in Amazon's International charts two months before its release date. The album features a duet with two-time Grammy Award winner Colbie Caillat, a cover of Van Morrison's "Have I Told You Lately That I Love You".
Harkin's second solo album, Mercy Street, was released in October 2015.[11] The songs on the album were written by Harkin and the album was self-funded. Harkin recorded all the songs on the album live in one take.[12]Mercy Street reached number one on the World Music Billboard charts.[13]
Harkin released a solo Christmas album titled Nollaig in 2016 which also reached number one on World Music Billboard charts. It was produced by Brian Byrne and recorded at his home studio. The album contains a mix of original and traditional songs, and features the Bulgarian Symphony Orchestra on several tracks.[14]
Harkin's eighth studio album, Man of Many Hearts, was released in the fall of 2022.