The teenager had been training with the club and playing with its U-23 side, but was not allowed to actually sign a professional contract until his 18th birthday.
Sargent turned 18 on Feb. 20 and has now put pen to paper, making him a Bremen player.
“All the formalities have been completed and Josh has now signed his professional contract with us,” Bremen CEO of football Frank Baumann said in a statement. “We’re really happy that he has decided to take this next step in his career at SV Werder Bremen. He has really impressed us since the beginning of this year and has gathered experience in first team training as well as some games with the Under-23s.”
The striker had interest in the U.S. but decided to pass on signing with Major League Soccer in order to pursue a chance to play in Europe.
Sargent has been training with Bremen since January, but could not be added to the roster because of a FIFA rule prohibiting non-European players from signing with European clubs until their 18th birthday. Fellow American teenager Christian Pulisic, who joined Dortmund at age 16, was able to get around that rule because of his Croatian ancestry.
Because Sargent's signing happened after the January window, the earliest the teenager can feature for the Bremen first team is in the 2018-19 season.
Sargent featured for the U.S. youth national teams at a pair of World Cups in 2017. He scored three times in five games for the U-17 side in India and found the net four times in five games at the U-20 World Cup in South Korea.
His performances at the youth level earned Sargent a call up to the U.S. senior national team in November 2017 despite not yet playing a minute of professional soccer. Though he was on the roster, he did not enter the 1-1 draw with Portugal.