He played college football for the Maryland Terrapins and was selected 12th overall by the San Diego Chargers in the 2005 NFL draft.

[4] Merriman was selected in the first round (12th overall) in the 2005 NFL Draft out of the University of Maryland by the San Diego Chargers.

Manning had made it clear he was not interested in playing for the Chargers, in a similar fashion to John Elway in 1983 when selected by the Baltimore Colts.

[9] Merriman started off his 2005 rookie year on the inactive list and completed a 10-day hold out from training camp.

It was during this game that Shawne Merriman garnered much national media coverage and in the following week made the Pro Bowl.

On October 22, 2006, reports were made public by CNN that Merriman would face a 4-game suspension for violating the NFL's steroid policy.

Subsequently, Cornwell stated that he believed the substance his client tested positive for was the anabolic steroid nandrolone, and that Merriman claimed it must have been in a tainted nutritional supplement he took regularly.

Merriman went on to record 8.5 sacks and make ESPN's midseason All-pro team,[17] prior to dropping an appeal against an NFL enforced 4-week suspension due to testing positive for steroids.

Merriman finished third in the balloting for 2006 Associated Press Defensive Player of the Year, behind Jason Taylor and Champ Bailey, after having tested positive for using steroids which is against the league's drug abuse policy.

Merriman reportedly responded by sending Taylor a "Lights Out" t-shirt and a box of popcorn with a note saying enjoy watching him in the playoffs.

[19] In week 4, however, Merriman performed the dance after sacking Kansas City Chiefs quarterback Damon Huard.

His prowess was shown during the season when it was said that his 9.5 sacks through to week 13 was seen as a decline in performance, a quote to which Merriman took a great compliment.

Merriman withheld his decision whether or not to play while seeking several different professional opinions, including that of well-known surgeon James Andrews of Birmingham, Alabama.

ESPN's Mike Tirico reported in the Chargers' Monday Night Football game that Merriman went to Miami, Florida to get a final opinion on his knee.

[citation needed] On August 13, 2010, after two weeks of hold out, Shawne Merriman signed tender and reported to camp.

[citation needed] On October 13, the Chargers announced that Merriman was being placed on injured reserve and, per NFL rules, would be released when he became healthy.

[13][22] On October 25, 2011, Merriman was placed on Injured Reserve list for the second consecutive season after suffering a partially torn Achilles tendon.

Merriman's former girlfriend, reality TV star Tila Tequila, claimed in an arrest complaint[33] that he choked and restrained her when she tried to leave his home.

[35] In December 2009, Merriman filed a civil suit against Tequila, alleging intentional interference with contract, unfair competition, and trademark infringement.

He claimed that Tequila improperly used his own "Lights Out" logo and disrupted negotiations for T-shirts to be marketed by Wal-Mart.

In the suit, Fattorini's parents claim their daughter sent texts earlier that night saying Merriman poured something in her drink.

They now believe that something was GHB - a powerful depressant commonly referred to as “the date rape drug.”[39] When paramedics arrived midday July 21, 2017, they found Fattorini unresponsive on the floor, half-naked, “with her jeans unzipped and unbuttoned, as though someone had tried to pull her jeans on to her body before the police or paramedics arrived.” Her bra was twisted.

[40] The coroner did not perform a sexual assault exam; by the time an LASD detective requested one, “in light of additional information he had received,” it was no longer possible.

On October 10, 2007, Merriman was chosen as the cover athlete for EA Sports' NFL Tour video game.

He showed off his tattoos in PETA's "Ink Not Mink" campaign, encouraging people not to wear animal furs.

[47] In January 2015, Japanese martial arts event GANRYUJIMA announced that they were negotiating with Merriman for him to be a fighter, but they were unable to reach an agreement.

[51] In April 2019, Merriman announced that he is starting his own MMA promotion, Lights Out Xtreme Fighting, which is expected to have its inaugural event on May 11, 2019.