The defender has played a key role at St Mary's in the last few weeks as he helped them move up to 11th in the Premier League table.
A win over Everton and a draw against Bournemouth has given the Saints squad a lift and Soares was able to beat Charlie Austin, Ryan Bertrand and Pierre-Emile Hojbjerg in the supporters vote.
The Portugal international has now won the award for the first time and he believes the backing from the fans has been crucial.
He told the club's official website: "It’s very good. It’s my first time for Southampton and I’m very happy because it means the fans are always supporting us as a team and in this case me as well.
"It was a tough month and we had some tough games. We didn’t always get the best results but the team reacted well and in these difficult moments, you need to show courage, go out there and still play football.
"The team had a very good reaction. I want to mention the game against Everton. I think all the staff, the team and the fans were together; we are much stronger like this.
"Our fans are very important now in a busy moment, with lots of games and they can give us the push we need to win more games."