Oakman attended Penn Wood High School in Lansdowne, Pennsylvania. He played both football and basketball. He committed to play college football at Penn State University in July 2010.

Oakman was redshirted as a true freshman at PSU in 2011. In February 2012, Oakman was dismissed from Penn State for violation of team rules. On Monday, May 13, 2012, after multiple messages by head coach Bill O’Brien, he was told that he was dismissed from the Nittany Lions football team. He transferred to Baylor University in July 2012.

As per NCAA transfer rules, Oakman took the entire 2012 season off. Oakman played in 13 games as a backup defensive end in 2013. He recorded 33 tackles and two sacks. In his first year as a starter, Oakman had a breakout season in 2014. He finished the season with 25.5 tackles for loss and 11.0 sacks. He earned third-team All-America honors from the Associated Press and was a consensus All-Big 12 selection. Oakman was projected by some analysts and scouts to be a first round pick in the 2015 NFL Draft. Instead of declaring for the draft, he decided to return to Baylor for his senior season. In 2015, Oakman was not able to match his successful 2014 season. He recorded only 4.5 sacks in 2015.

At the Cotton Bowl Classic on January 1, 2015, a picture of Oakman on the jumbotron at AT&T Stadium went viral across social media, including social media site Twitter. The image became “an internet sensation” overnight because of his intimidating build, with Oakman standing at 6 ft 9 in (2.06 m).

Several early mock drafts projected Oakman to be a first round pick in the 2016 NFL Draft. Chris Burke of Sports Illustrated penciled in Oakman as the first overall pick in his “2016 NFL Mock Draft 1.0,” which was published a few days after the conclusion of the 2015 NFL Draft. Oakman’s production dropped in 2015 and his draft stock fell throughout the season. One AFC area scout commented that he would not select Oakman in the first three rounds of the draft. Some of the concerns about Oakman were his skinny lower body, lack of pass-rush technique, and “inconsistent motor chasing plays and inability to make plays against better competition.” After Oakman’s arrest on a sexual assault charge, which occurred only two weeks before the 2016 NFL Draft, an NFC executive told Lance Zierlein of NFL.com that Oakman was “undraftable now” because the case is unlikely to be resolved before the start of the draft. Zierlein believed the arrest would likely result in Oakman being removed from all NFL team boards.

Oakman went undrafted in the 2016 NFL Draft. After the draft, he wasn’t expected to get signed as an undrafted free agent due to the legal issues he was facing at the time.

On April 13, 2016, Oakman was arrested in Waco and charged after a woman accused him of sexual assault. According to a police affidavit, Oakman met the accuser at a bar and asked if she wanted to go to his off-campus residence. They walked to Oakman’s duplex where, according to the woman, he forced her into a bedroom, forcibly removed her clothes, forced her onto the bed, and sexually assaulted her. On July 20, 2016, a grand jury in McLennan County indicted Oakman on charges of second-degree felony sexual assault. The trial of the case began February 26, 2019. On February 28, 2019, after the jury deliberated for 45 minutes, Oakman was found not guilty of sexual assault. The jury cited evidence for consensual sex and the lack of incriminating evidence for their decision.

In November 2017, Oakman signed with the Triangle Torch of the American Arena League.

On March 8, 2018 Oakman signed with the Bismarck Bucks of Champions Indoor Football.

On April 6, 2019, Oakman signed with The Spring League and was assigned to the Austin Generals.

In June 2019, Shawn Oakman signed with the West Virginia Roughriders of the American Arena League.

On October 16, 2019, Oakman was drafted to the Los Angeles Wildcats of the XFL. He was waived on December 17, 2019. The Wildcats re-signed Oakman on January 24, 2020. In his debut game, Oakman had a sack and a pass deflected. He had his contract terminated when the league suspended operations on April 10, 2020.