In February 1973, Ulrich’s father obtained passes for five of his friends to a Deep Purple concert held in the same Copenhagen stadium as one of his tennis tournaments. When one of the friends could not go, they gave their ticket to the nine-year-old Lars, who was mesmerized by the performance and bought the band’s album Fireball the next day. The concert and album had a considerable impact on Ulrich, inspiring the start of his music career.

In the documentary Anvil! The story of Anvil, Ulrich states that witnessing a Y&T show was his defining moment in deciding to become a musician. In 1981, he discovered British heavy metal band Diamond Head. He was excited about the band’s style of music after purchasing their debut album Lightning to the Nations, and traveled from San Francisco to London to see the band perform live at the Woolwich Odeon. Ulrich remains a fan of Diamond Head and would later mix their album The Best of Diamond Head. Upon returning to America, Ulrich placed an advert in a local classifieds newspaper looking for musicians to start a band with him. James Hetfield replied to the ad, and Metallica was formed.

Later in 1981, Ulrich met James Hetfield in Downey, California, and they formed the heavy metal band Metallica. He got the band name from a friend, Ron Quintana, who was brainstorming names for a heavy metal fanzine he was creating, and Metallica was one of the options, the other being “Metal Mania.” Ulrich encouraged him to choose Metal Mania, and used the name Metallica for himself.

Ulrich has been married three times. His first marriage was in 1988 to Debbie Jones, a British woman he met on tour, but they divorced in 1990 due to Ulrich’s constant absence during the recording of the 1991 album Metallica as well as his alleged infidelity. His second marriage was to Skylar Satenstein, an emergency medicine physician, from 1997 to 2004. They had two sons before divorcing.

Between 1998 and 2002, Ulrich tried running a record label, the Music Company. The company was a joint venture with Metallica accountant Tim Duffy. It failed to catch on and folded in the spring 2002. His voice can be heard in the opening seconds of “Leper Messiah” and he also counts to four in his native Danish on the “St. Anger” music video. To unwind after some gigs, Ulrich listens to jazz.

In April 2000, Ulrich became a vocal opponent of Napster and file sharing as Metallica filed a lawsuit against the company for copyright infringement and racketeering. In July 2000, he testified before the Senate Judiciary Committee after Metallica’s entire catalogue, including the then-unfinished track “I Disappear” was found to be freely available for download on the service. The case was settled out-of-court, resulting in more than 300,000 Napster users being banned from the service. Ulrich was quoted by LAUNCHcast as having some regrets:

Ulrich also has a passion for fine art. In 2002 Ulrich sold a painting from his own collection, “Self Portrait” by Jean Michel Basquiat, 1982. With a pre-sale price estimate of $5 million, it ultimately sold for triple that at Christie’s Auction House. At the 2016 Men in Blazers Night of the Golden Blazer, Ulrich revealed his passion for Chelsea Football Club, as he stated that he went to Stamford Bridge many a time starting in 1973 during the time his father was playing at Wimbledon during the Tennis Season.

Ulrich is a fan of a wide variety of genres, feeling particularly passionate about jazz music. He is particularly inspired by the influential tenor saxophonist Dexter Gordon, who was Ulrich’s godparent. Ulrich, a friend of Noel Gallagher, is a fan of Gallagher’s former band Oasis and claimed Gallagher was his inspiration to give up cocaine in 2008. Ulrich has also expressed his desire to sometime play drums in Gallagher’s band Noel Gallagher’s High Flying Birds. According to Gallagher, the first autograph he did in America was for Ulrich.

When Ulrich and fellow Metallica members James Hetfield, Jason Newsted, Cliff Burton, Kirk Hammett, and Robert Trujillo were inducted into the Rock and Roll Hall of Fame in 2009, Ulrich was the first Dane to receive the honor.

He made his acting debut in the HBO original film Hemingway & Gellhorn, which began filming in March 2011 and was released on 28 May 2012. Ulrich made a brief cameo appearance as himself in the film Get Him to the Greek, as the partner of the character Jackie Q. In 2012, Ulrich was the focus of the documentary film, “Mission to Lars”. The film by Kate and Will Spicer concerns their journey with their brother Tom, who lives in a care home in Devon, England and who has Fragile X syndrome, to try to meet Ulrich at one of Metallica’s 2009 gigs in California.

In 2013, Ulrich used his silver drum kit that he used from the period 1996–2003 on a secret show on the Orion Music + More Festival when Metallica played as the band ‘Dehaan’

Following his divorce from Satenstein, Ulrich dated Danish actress Connie Nielsen from 2004 to 2012. They had one child together. He married American fashion model Jessica Miller in 2015.

Having led a campaign for several years to get his longtime favorite band, Deep Purple, inducted into the Rock and Roll Hall of Fame, Ulrich delivered the induction speech when the band went into the Hall in 2016.

Ulrich was knighted in his native country of Denmark. He was awarded the Knight’s Cross of the Order of the Dannebrog on 26 May 2017 by Margrethe II.