Nolan was replaced by assistant head coach Mike Singletary, who will step in as head coach for the remainder of the season.
"This decision was difficult because Mike has been both a friend and valued coach of our team." said 49ers general manager Scot McCloughan. "I have a great deal of respect for Mike and his family. But my first obligation is always to do what is in the best interest of our fans and the entire 49ers organization. It is for this reason that we've made the decision to give the head coaching role to Mike Singletary."
The 49ers suffered a 29-17 road loss to the New York Giants this past Sunday, dropping their record to 2-5.
The 49-year-old Nolan, who was in the fourth season of a five-year contract with the 49ers, compiled an 18-37 record during his tenure with the team. The best finish under his watch was 7-9 in 2006.
In fact, the 49ers haven't had a winning record since 2002, when they went 10-6 before falling to Tampa Bay in the divisional round of the playoffs.
Nolan was hired by the 49ers on January 19, 2005, 37 years to the date his late father, Dick, was hired by the team. Dick Nolan, who passed away last November, captured three straight NFC West championships (1970-72) in San Francisco.
The 50-year-old Singletary is in his fourth year with the 49ers. A 10-time Pro Bowl selection as a Chicago linebacker, Singletary was inducted into the Hall of Fame in 1998.
"I am confident that Mike Singletary's leadership ability along with his experience as both a Hall of Fame player and coach gives him the ability to turn our season around," continued McCloughan.
Reports surfaced earlier Monday that the 49ers would fire Nolan after the team hosts Seattle this coming Sunday. They have a bye after that game.