Since joining the club in 2010, the New Zealand international has established himself as a key man at the back, with 204 appearances being made in all competitions.
The Hammers have now moved to reward Reid for his consistency and commitment by handing the central defender a deal which runs until 2023.
The 29-year-old told the club's official website: "I'm very happy. I'm pleased we've got it sorted so I'm obviously looking forward to the seasons ahead. It's going to be a big amount of time I've spent at the club and I'm looking forward to it.
"I've been here a long time now! I think with the business we've done over this summer and the players we had here before, I think we can go on to have a good season and seasons ahead. It's all about trying to get better.
"I enjoy being here and my family does as well so I'm very happy I'm able to stay here."
At the end of the 2012-13 campaign, Reid won the club's player of the year accolade.