With the deal complete, Moultrie now becomes the youngest player ever to sign with an NWSL side.
Moultrie made headlines in May when she filed an antitrust lawsuit challenging the NWSL and its rule of prohibiting players under 18. The lawsuit had argued that the league's age rule violated the Sherman Antitrust Act and also hindered Moultrie's career development and chances of reaching the U.S. national team.
The NWSL stated that the age issue should be part of the ongoing collective bargaining agreement (CBA) talks with the NWSL Players Association. U.S. District Judge Karin J. Immergut granted a preliminary injunction earlier this month, which prohibited the NWSL from enforcing the age rule and cleared a path for Moultrie to sign with a team.
"Every coach has always told me there's a lot you can do in training, but where you really grow and mature as a player is in games,'' Moultrie said. "And for that to finally be here, for me to take that next step and just continue to grow as a player, like I said multiple times it's just very exciting and I know this is where I'll be able to grow the most.''
"We are pleased to have Olivia join our team," said Gavin Wilkinson, Thorns general manager and president of soccer. "She has been part of this club since early 2019 and there have been many Thorns staff fully invested in her development."
"This step is very important for Olivia," said Thorns head coach Mark Parsons. "For this club to have the commitment and vision to sign a young, talented player that we really believe in is immense. Olivia has continued to grow and push forward throughout her time here and has taken every challenge and turned it into an opportunity."
The NWSL said in a statement: "After the development of a comprehensive minor player protection plan and execution of a SPA, special addendum, and parent guaranty, the NWSL welcomed Olivia Moultrie into the league today. The NWSL continues to believe that age requirements for the league should be collectively bargained [as they are in other leagues] and those negotiations are ongoing."
Moultrie has been training with the Thorns since she was 13, and has participated in scrimmages and preseason games against other professional teams. The Thorns play Racing Louisville on Saturday.
The Thorns acquired the rights to Moultrie from OL Reign, the first team on the NWSL Discovery Priority list, in exchange for a third-round pick in the 2022 NWSL Draft.
Moultrie was born in California, and she has been touted as a soccer phenom from a young age. She was offered a scholarship to the University of North Carolina -- which has won 21 NCAA titles and produced dozens of U.S. women's national team players -- at age 11.
But she turned that down at age 13, hiring sports media company Wasserman Media Group to represent her and signing a nine-year, six-figure endorsement deal with Nike. Her family has since relocated to Portland.
At the U.S. youth national team level, Moultrie was most recently in camp with the U-17 women's national team in February 2020 as part of a 24-player roster for training camp.
The youngest signing ever in Major League Soccer was Freddy Adu at age 14. Another 14-year-old, goalkeeper Emmanuel Ochoa, was signed to a Homegrown Player contract by the San Jose Earthquakes in 2019.
There are age limits for other men's professional leagues in the United States. Players have to be 18 to sign with an MLB team (17 for internationals), 19 for the NHL and 19 for the NBA. NFL players have to be out of high school for at least three years.
WNBA players have to be 22 by Dec. 31 of the year they're drafted.