After scoring 15 goals last season, the Norwegian had the attention of many big clubs. It was Tottenham who won the battle for the striker.
Her contract with Hammarby expired at the turn of the year, meaning she will join her new club for free.
The 24-year-old has previously played for Manchester City, but never really made a name for herself in England during that time.
"This is a fantastic club, so I'm really looking forward to getting started. The club focuses on development, which is very important to me," Blakstad said on Tottenham's website.
At Tottenham she will become teammates with several Swedes: Matilda Vinberg, Josefine Rybrink, Hanna Wijk and the sisters Amanda and Matilda Nildén.
In 75 competitive matches for Hammarby, Blakstad scored 36 goals.
