After 11 seasons with the Phoenix Mercury, 10-time WNBA All-Star Brittney Griner has agreed to a one-year deal with the Atlanta Dream, sources told ESPN on Tuesday.

Griner, who has spent her entire career in Phoenix after being drafted No. 1 overall in 2013, heads to Atlanta in one of the most stunning free agency signings in league history.

Griner announced the move in a video posted to Instagram on Tuesday night. The signing can't be made official until Saturday, when contracts are allowed to be signed.

"So, free agency has been everything I wanted it to be," Griner said in the video. "I was able to find where I wanted to go. And honestly, what led me to that decision ultimately was the team, the players, as individuals, and then also my family."

Griner's departure marks the beginning of a new era for the Mercury, who could also be without Diana Taurasi for the first time in two decades if she decides to retire. Taurasi and Griner won the franchise its third and most recent championship in 2014.

"You know it was a hard decision," Griner said, "you're leaving what you know, what I've known for my whole career. But there's also the exciting factor of like, OK, this is a rebrand now, I get to show them something different."

The 6-foot-9 center missed the 2022 campaign when she was wrongfully detained in Russia for nearly 10 months. She was eventually freed in a high-profile prisoner exchange and returned to All-Star form in 2023 and 2024.

Griner, a six-time All-WNBA selection, goes to Atlanta as the biggest free agent signing in franchise history. She joins a team also headlined by Rhyne Howard, drafted first overall by the Dream in 2022, and Allisha Gray, for whom Atlanta traded for in 2023. The franchise moved on this offseason from former coach Tanisha Wright and hired Karl Smesko from Florida Gulf Coast University to lead the team.

The Las Vegas Aces also looked at signing Griner, sources told ESPN's Ramona Shelburne, in their long-standing effort to find another big to play alongside A'ja Wilson. But after acquiring former Seattle Storm guard Jewell Loyd and evaluating their style of play moving forward, sources said the Aces have turned their attention to other post players such as Cheyenne Parker-Tyus and trying to re-sign veterans Tiffany Hayes and Alysha Clark.

Earlier Tuesday, the Mercury also finalized a deal to acquire five-time All-Star Alyssa Thomas and Ty Harris from the Connecticut Sun, sources told ESPN, a trade that will send Natasha Cloud, Rebecca Allen and the 2025 No. 12 pick to Uncasville.

According to sources, Phoenix is also expected to meet with Satou Sabally, who has requested a trade out of Dallas, and to speak with free agent DeWanna Bonner.

ESPN's Shams Charania contributed to this report.