On December 5, 2015 Little Mix announced during their set for the Jingle Bell Ball that "Secret Love Song" would be their next single before Jason Derulo joined them on stage to perform the song.
ANDPOP writer Rebecca Mattina stated: "Jason Deruuuulo! This is the collaboration we didn’t even know we needed but are forever thankful we now have. Prepare yourselves for a delicate yet powerful ballad –reminiscent of previous LM songs like “Towers.” Jason’s soulful voice is a perfect mirror to the girls’ and harmonizes with Perrie beautifully. Props to Leigh-Anne for killing that last chorus!" 
"Secret Love Song" debuted at number 66 on the UK Singles Chart on 8 January 2016, selling 8,635 units. The following week, it sold 14,964 units and rose to number 34. It peaked at number six, making it their eighth top ten single to date. On 1 April 2016, the song was certified gold in the UK for selling over 400,000 copies. The song peaked at number 16 in Australia and has been certified double platinum for selling over 140,000 copies despite not being released worldwide. As of August 2016 the song has sold over 800,000 copies worldwide, despite being a UK/Ireland only release with limited promo. It has been certified Platinum in Ireland, UK, Australia and New Zealand, becoming their second best selling single in the UK and their second Platinum single in their home country.
Secret Love Song found major success in Asia by peaking at number 1 in the Philippines on June 6, 2016. Secret Love Song peaked at 3 in Malaysia, 4 in Singapore, and at 7 in Indonesia. 
On December 5, 2015 Little Mix were joined by Jason Derulo to perform the song during the Jingle Bell Ball.
On February 5, 2016 Little Mix joined Jason Derulo on his London tour to perform the song with him. They performed it at the 02 Arena.
The music video was filmed in London, England. It was directed by Frank Borin and was due to be released on January 28, 2016. It was postponed to the February 3, 2016.