'Cosmic Love' was a joke title, but it stuck. The most hungover I’ve ever been when writing a song. I went to [Isabella Summers's] studio after having been to a party, and I was lying on the floor wanting to vomit. We were working really hard on a song and just trying to make this sh*t piano part work, and all of a sudden I hit on one note, and I’d got it. We wrote the whole song in ten minutes.
"Cosmic Love" has been widely praised, with many reviews calling it the best track on the album. Pitchfork Media says the song is "audaciously huge" and one of the album's "finest" tracks, alongside "Blinding".
A promotional music video for the song was shot on 24 March 2010. Welch's manager Mairead Nash described it as "amazing." The video was debuted on the band's official website on 11 May 2010.
The music video begins with a shot of a lightbulb flashing. Welch is then seen to walk through some trees with autumn leaves, and a light falls into her eye, making her scream. The video then moves on to show Welch lying on the floor in a black outfit, in a mirrored room filled with different coloured lights around her. She then stands up and dances in the room. The video then moves back to Florence walking through the autumn leaves, with blue, green and purple lighting shining on her, and she appears to be lost as she is surveying her surroundings. The scene of Welch in the room of lights then changes to darker lighting, and her outfit changes into a white dress with lights. Later in the song, during this scene, leaves are seen to surround her as she is dancing. The video ends with Florence taking the light from inside her chest, and releasing it into the air, and it floats into the lightbulb which started the video.
"Cosmic Love" debuted on the UK Singles Chart at number 162 on 26 June 2010 before climbing to number 116 the following week. On 11 July 2010, following the physical release of the single, it rocketed into the Top 100 at number 51, giving Florence her seventh Top 100 hit from the album Lungs. "Cosmic Love" is Florence's second least successful single in the UK charts behind "Drumming Song", along with "Kiss with a Fist", which also peaked at number 51. Conversely, the song is Florence and the Machine's highest charting song in Ireland, as due to high digital sales it charted at number 3 there, almost a year before its physical release after it was featured in an advert for The O2 in Dublin.