The 38-year-old was appointed as manager in August 2012 and led the club to 10th in League One in his first season in charge.
Barker's dismissal has come after a run of seven matches without a win.
"Crawley Town Football Club can confirm that it has terminated the contract of first team manager Richie Barker with immediate effect," read a statement on the club's official website.
"The club will make an announcement as soon as possible on who will look after team affairs in the interim period and we ask our supporters to have patience while the process of finding a new manager is undertaken."
Crawley lie 12th in League One after taking 22 points from 18 matches.