Lovett was born in Woodbury, Long Island to a Reform Jewish family of Ukrainian ancestry that operated a box factory started by his grandfather. He attended Syosset High School. Lovett graduated from Williams College in 2004 with a degree in mathematics. His senior thesis, Rotating Linkages in a Normed Plane led to a related publication on the same topic in American Mathematical Monthly. Lovett was also the 2004 Williams College Class Speaker at his commencement. After graduation, Lovett spent a year working as a paralegal and doing stand-up comedy on the side.

In 2004, Lovett volunteered for John Kerry’s presidential campaign. He was asked to write a statement for the candidate, and his work led to an offer of a writing internship. Then, he briefly worked in Jon Corzine’s Senate office. He was hired in 2005 to assist Sarah Hurwitz as a speechwriter for then-Senator Hillary Clinton, and he continued to write speeches for her through her 2008 presidential campaign.

Before Barack Obama ran for reelection, Lovett moved to California to become a screenwriter, citing a desire to write independently and focus on creative comedy full-time. Lovett collaborated with Josh Gad and Jason Winer on the television series 1600 Penn, of which Lovett was a co-creator, executive producer, and writer from 2012 until its cancellation in 2013. Lovett then worked as a writer, producer, and advisor on season three of HBO’s The Newsroom. From 2012 to 2015, Lovett also contributed opinion pieces to venues like The Atlantic.

Starting in March 2016, Lovett co-hosted The Ringer’s political podcast Keepin’ it 1600 with former fellow Obama staffers Jon Favreau, Dan Pfeiffer, and Tommy Vietor. The podcast was intended to cover the 2016 presidential race, and not expected to continue after that. But after the November 2016 election, Lovett, Favreau and Vietor wished to become engaged in politics again without having to leave Los Angeles or return to political campaigning. So they founded a liberal media company, Crooked Media, with the flagship podcast Pod Save America. Crooked Media, and Pod Save America in particular, has been compared to previous left-wing efforts like Air America to match America’s Conservative talk radio, and Lovett has been characterized as providing comic relief to the programming. The company has since launched a range of podcasts, several of which regularly feature Lovett.

In March 2017, Lovett began hosting Lovett or Leave It, a panel show podcast produced by Crooked Media. The podcast is typically recorded in front of a live audience in Los Angeles, but Lovett and Crooked Media have embarked on national and international tours featuring live versions of both Pod Save America and Lovett or Leave It. Lovett was also involved in launching Crooked Media’s voter recruitment and education project, Vote Save America.

Lovett is gay. He and Pulitzer Prize-winning investigative journalist and author Ronan Farrow have been romantically involved since 2011. In October 2019, Farrow published Catch and Kill, where he publicly announced their engagement, having proposed to Lovett in an earlier draft of the book.