The Dutchman has signed a 'multi-year contract' with the team and will succeed Gerardo Martino.
De Boer won four successive Eredivisie titles during his time in charge of Ajax, but struggled to replicate his success during a disastrous three-month spell at Inter in 2016.
He took charge of Palace for the 2017-18 campaign, but was sacked when the Eagles lost their first four Premier League games.
However, he has now been handed a chance to revive his career in the United States, and Atlanta president Darren Eales is delighted to have secured De Boer's signature.
“The club’s sportive ambitions, as set out in a long-term strategy to be the best in class, clearly fits my personal ambitions,” De Boer told the club's official website.
“I would like to build on the current success to develop a secure, solid foundation for the club at the top of MLS and beyond.
"Aside from the club’s ambitions, the values, culture and the philosophy for the entire organization are a vital part in realizing that point of success.
Atlanta United FC (@ATLUTD) December 23, 2018
"This is exactly what I believe in as a person and as a coach. All of this combined, makes that I am really excited to be a part of it.”
De Boer began his coaching career in 2008 with the Netherlands, where he was an assistant, before moving on to Ajax in December 2010.
Six years at the Amsterdam side yielded four Eredivisie titles, which caught the attention of Inter. At San Siro, though, he lasted only 14 matches before being sacked in November 2016, while his spell at Palace was aborted after only four Premier League matches – a record in the division for a full-time manager.
De Boer has been out of the game since that episode in London, which concluded on September 11, 2017.
Atlanta, meanwhile, are coming off a highly successful campaign, in which they claimed MLS Cup glory thanks to a 2-0 win over Portland Timbers.