The song will be performed at the ceremony in Copenhagen in May, and released on April 28 on the resurrected East West label.
Molly - full name Molly Smitten-Downes - will also perform the track during a Eurovision preview show at London's Café de Paris on April 13.
"As it says, I believe that we're all important in some way, and that we all have a part to play in something bigger," the singer said of the track.
"We just have to follow our heart and our instinct and see what happens."
Smitten-Downes, who was selected for Eurovision via BBC Introducing, added: "I want to change preconceptions of Eurovision and make people who think it isn't cool to think, 'This is actually quite good'.
"And I want the people of the UK to be proud of me. But Eurovision is part of my journey: it's not the journey itself."
Inspired by Max Ehrmann's poem Desiderata, the song is the first entirely self-written song by a UK entrant since Katrina and the Waves won in 1997 with 'Love Shine A Light'.
The digital release of the single will come packaged with an extended version and remix from Secaina Hudson.