Williams generated controversy this week during an appearance on Fox & Friends, where he appeared to compare Obama to Nazi dictator Adolf Hitler.
The musician said he disagreed with Republican Speaker of the House John Boehner's decision to play golf with Obama because it was "like Hitler playing golf with [Israeli prime minister Benjamin] Netanyahu".
The outcry over his remarks led ESPN to not use Williams's song 'All My Rowdy Friends Are Coming Over Tonight' in the opening of this week's edition of Monday Night Football. The track had served as Monday Night Football's theme tune for more than 20 years.
Williams later apologised and claimed that he hadn't expressed himself properly.
He wrote on his website: "I have always been very passionate about Politics and Sports and this time it got the Best or Worst of me (sic)."
Both ESPN and Williams said on Thursday that they'd decided to end their working relationship in the wake of the controversy.
Williams told The AP: "I have made MY decision. ... Me, My Song, and All My Rowdy Friends are out of here!"
'All My Rowdy Friends Are Coming Over Tonight' first appeared on Williams's 1984 album Major Moves.
Watch Hank Williams Jr's controversial comments below: