The 25-year-old, who was named the Hammers’ 2025/26 Hammer of the Year, agreed the new deal before returning for pre-season training.
“I’m really happy to sign a new contract with West Ham United,” Siren told West Ham media.
“I’ve really enjoyed my time at the Club over the last two years, so it was an easy decision to extend my stay. We have a really good group of players and staff, and I’m looking forward to continuing the journey with them.
“West Ham feels like the right place for me to continue developing as a player, and I’m excited to see what we can achieve together this season.”
Siren has made 54 appearances for West Ham since joining from Norwegian top-flight side LSK Kvinner in the summer of 2024.
After making her debut in a 6-1 victory over Portsmouth in the Women’s League Cup, she featured 26 times during her first season before representing Finland at UEFA Women’s Euro 2025.
Siren enjoyed an outstanding 2025/26 campaign, starting every Barclays Women’s Super League match and playing more minutes than any other player in the squad. Her strength in the tackle, tireless work rate and midfield quality have made her a key figure for the Hammers.