The song - from Labrinth's debut album Electronic Earth - is out to download now on iTunes.
It was the first time that Labrinth has performed the track live alongside Emeli, with both stars on the show this evening.
The singer, the only act not from a TV talent show signed to Simon Cowell’s music label, previously said he didn’t watch the series and claimed he was being "forced" to perform.
“I’ve been forced,” Labrinth was quoted as saying in The Sun. “A lot of people think I hate X Factor and think it’s s**t.
“I’m just being honest about the way it works. I think artists who take their craft really seriously don’t go on it.”
Labrinth kicked off this evening's performance, singing from behind his piano before introducing Emeli to the stage.
Watch Labrinth and Emeli on The X Factor below...