During his college years, Leff strayed from his intensely personal song-writing style and focused on writing and producing for other artists. But during his sophomore year, he stumbled upon an illuminating interview with Paul Simon, in which Simon described his song-writing approach as a process of uncovering his innermost buried feelings. The interview helped Leff to get in touch with the way he used to write.
Shortly after, Leff adopted the stage name Lauv, Latvian for 'lion'. This is a nod to his mother's heritage; his first name, Ari, meaning 'lion' in Hebrew; and to his own zodiac sign, Leo.
Then, while recovering from a break-up in 2014, he revealed his feelings through co-writing "The Other" with Michael Matosic.This was a fusion of rhythm and blues and indie-pop with influence from jazz guitar. He felt that the song was special to him, so he did not want to give it up to another artist. He released the song under his stage name. The song gained blog attention and went viral, peaking at number three on blog aggregator Hype Machine, and hitting the Global Top 100 on Spotify.
After graduating, Leff signed to the publishing company Prescription Songs.
In 2015, Leff released his debut EP, Lost in the Light, which featured "The Other".
Then, apart from releasing a single titled "Question" featuring Travis Mills, Leff worked on writing and producing songs for other artists. Most notably, he co-wrote and co-produced "No Promises" for Cheat Codes and Demi Lovato.
On May 19, 2017, Leff released the single "I Like Me Better", an up-tempo track which also achieved popularity. The song was inspired by his relationship which started two months after he had first moved to New York City to further his studies.
In the same year, he headed his own Late Nights, Deep Talks tour in which he performed in 8 cities across the United States. The tour began on May 23 in Los Angeles and concluded on June 7 in New York City. On July 9, he also performed in Summerfest in Milwaukee, Wisconsin.
It was announced on September 4, 2017, that Leff would be joining Ed Sheeran as the supporting act on his Divide Tour in Asia