Mariotti was born in Pittsburgh and studied journalism at Ohio University before beginning his professional sportswriting career at The Detroit News. In 1985, Mariotti became one of the country's youngest sports columnists at The Cincinnati Post. He moved on to write columns for The Rocky Mountain News and The Denver Post. He then wrote for The National Sports Daily in New York.
Mariotti started writing for AOL Sports on January 5, 2009, where he shared his views about any number of sports-related topics. In 2010, he left Chicago and relocated to Los Angeles.
In 2010, ESPN announced it was no longer employing Mariotti due to his arrest on charges of domestic abuse.
On February 10, 2013, Jay Mariotti announced that he was returning to ESPN to work on "a freelance storytelling” assignment.
Mariotti joined the Chicago Sun-Times as a sports columnist in 1991 and spent 17 years there. He feuded with everyone from colleagues to Chicago White Sox manager Ozzie Guillén, the latter of which prompted Sun-Times baseball writer Chris De Luca to write, "The same critics who avoid ever stepping into the White Sox's clubhouse are calling the Chicago media soft for not skewering manager Ozzie Guillén. They want Guillen fired yesterday. Sounds tough, but the rhetoric comes up a little, well, soft." On August 26, 2008, Mariotti announced that he was resigning from the newspaper. He stated his choice was heavily weighted on the fact that, while covering the 2008 Summer Olympics in Beijing, he saw more writers for websites covering the Games and a smaller presence of newspapers, giving him the opinion that writing for a website was "what the future holds." Mariotti's criticism of the newspaper industry and his resignation from the newspaper prompted a public rebuttal from another fellow Sun-Times employee, high-profile movie critic Roger Ebert, who defended the newspaper business and criticized Mariotti's penchant for writing sensationalist columns to attract readers.
In August 2013, Mariotti launched a short-lived internet venture called The Mariotti Show on www.mariottishow.com in a distribution deal with Genesis Communications, a partner of the NBC Sports Radio Network. The site featured the live streaming feed of his national radio show and highlighted his columns on major sports topics and events, immediate short-form opinions about sports and life, interviews, video commentaries, a running travelogue and free-flowing audience interaction. In November 2014, operations ceased because of marketing and financial challenges.
In April 2015, The San Francisco Examiner hired Mariotti to be its lead sports columnist as part of an expanded sports package. In March 2016, Mariotti and the Examiner parted ways.
In January 2017, Mariotti and fellow Around the Horn panelist Woody Paige launched a daily sports podcast titled "Unmuted".
On the morning of August 21, 2010, Mariotti was arrested in Los Angeles, and released on $50,000 bond. On September 13, Los Angeles city prosecutors charged Mariotti with seven misdemeanors in connection with the domestic disturbance. On September 30, Mariotti pleaded no contest to a misdemeanor battery count and was sentenced to 3 years probation and 40 days of community service. The charge was later expunged.