The song is a mid-tempo indie pop ballad with elements of alternative music, set to a beat of 76 BPM. It is composed in the key of A Major, with the vocal range spanning from E3 - F♯5. Mike Wass of Idolator described the production on the song as the most expansive of Barielles's career, with its incorporation of "kooky staccato beats" and a "sprinkling of synths". Its lyrics describe the act of falling in love and the "beautiful start / to a lifelong love letter".
The music video for "I Choose You" was directed by Dennis Liu and was released on May 5, 2014. It features two real-life couples - one heterosexual and one lesbian - delivering unique proposals to their significant others with Bareilles's assistance. The video combines footage of the preparations with shots of Bareilles singing, and culminates in the proposals.
"I Choose You" debuted at No. 36 on the Adult Pop Songs chart for the week of March 1, 2014, and debuted at No. 27 on the Adult Contemporary chart for the week of April 26, 2014. It has since reached the Top 20 on both charts. The song also debuted at its peak position of 81 on the BillboardHot 100 for the chart dated May 24, 2014.