The striker scored 17 goals in the Swedish women's league last year.
Earlier in January, Aftonbladet reported that the parties had been negotiating for a long time and that Wangerheim was close to a move to English Women's Super League club Manchester United.
Hammarby confirms on its website that the transfer is complete.
According to Fotbollskanalen, Hammarby will receive around 7 million kronor for the transfer, the largest in Swedish and Nordic women's football. The 21-year-old will also receive a signing bonus and around 450,000 kronor in monthly salary, a top salary at United.
"Ellen has been a fantastic representative for the club. The transfer was hotly debated this summer, but she chose to stay for the rest of the year and continue to develop in our environment. We wish her all the best going forward and are proud to make such a big sale. It sets the bar for others in the future," says sports director Arnór Smárason on Hammarby's website.
Anna Sandberg, Hanna Lundkvist, Julia Zigiotti Olme and Fridolina Rolfö already play for United.
