The Watford four-piece beat solo singer Grace Davies in the final, which saw both acts perform original songs for the first time since the show launched in 2004.
Rak-Su thanked viewers for voting for them and their families, while their mentor, Simon Cowell hailed them as “stars”.
Following their win, Jamal from the band said they were “speechless”. He said: “I just want to thank everyone at home, everyone here, all my friends and family who made this special.”
Simon Cowell added: “I want to say first of all congratulations to Grace who is really an outstanding artist.
“Obviously to the guys, Rak-Su, you are gentleman, stars and to everyone that voted thank you.”
Rak-Su’s win victory was slightly overshadowed by the show’s poor ratings.
Despite being brought forward so as to not clash with the ‘Strictly Come Dancing’ final, overnight figures for Saturday’s final show pulled in an average of just 4.4 million views, compared to Strictly’s 9.9 million.
The average on-the-night viewing figure is 1.1m down on the Saturday night of the 2016 final, which until this year was the least-watched X Factor final in series history.
Meanwhile Rak-Su’s debut single, ’Dimelo’, has been released and features guest appearances from Wyclef Jean and Naughty Boy.
The single will raise money for two chlidren’s charities, Together For Short Lives and Shooting Star Chase.