The Dutchman will replace Tata Martino, who announced in October that he will leave Atlanta after winning his first club title.
De Boer, 48, a former defender of the Netherlands, Ajax Amsterdam and Barcelona, worked in the English Premiership with Crystal Palace but only lasted for four games in the league.
New chapter. Same mission.#ATLUTD name @FdeBoerOfficial as 2nd head coach in club history
? https://t.co/H2VX85UytQ pic.twitter.com/AT7rLstHHf
— Atlanta United FC (@ATLUTD) 23 décembre 2018
However, it was his record of developing the rising players in Ajax that impressed the American club.
"Frank De Boer has a great background both as a coach and player and we look forward to welcoming him to the club," said Atlanta president Darren Ellis in a statement: "When we started our research, we were very determined to find someone who met all the standards we set.
The views The philosophical about how to play matches our views without a doubt.
"He has a great track record in the development of the rising players, many of whom have become stars in the European teams," he said, adding that his language skills, which include Spanish and English, will ensure a smooth transition of leadership at the club level.
OK, he could really play ?? pic.twitter.com/XzkHhNUgWP
— Atlanta United FC (@ATLUTD) 23 décembre 2018
De Boer, one of the country's most outstanding defenders, has participated in the World Cup twice and the European championship three times with the Netherlands.