At age 17, Rheon joined the Welsh language soap Pobol Y Cwm, in which he originated the role of Macsen White, but later left to train at the London Academy of Music and Dramatic Art.

Also in 2008, he was cast as the haunted Moritz Stiefel in the London production of the Tony Award-winning rock musical Spring Awakening.

[6] He played this role from January 2009 at the Lyric Hammersmith and continued when the show was transferred to the Novello Theatre, until it closed in May 2009, five months earlier than planned.

He earned a What's on Stage Award nomination for Best Supporting Actor in a Musical, which was eventually won by Oliver Thornton (Priscilla Queen of the Desert).

[6] Immediately after Spring Awakening, Rheon was cast in the E4 channel's Misfits, a BAFTA winning programme that was described by 247 Magazine as "a mix of Skins and Heroes".

Rheon also made two guest appearances as the character Ben Theodore in Simon Amstell's comedy Grandma's House.

In 2010, he recorded his first solo work, Tongue Tied EP, at RAK Studios in London,[15] produced by Jonathan Quarmby and Kevin Bacon.

He returned to RAK Studios, in April 2011, to record his second EP Changing Times, again produced by Quarmby and Bacon, with the addition of three backing musicians.

[18] Music journalist Neil McCormick described the album as "an absorbing collection of moody, introspective songs, all written by Rheon, who plays acoustic guitar with a deft touch and sings in an expressive, gritty voice".