The Dutchman has been under increasing pressure following the Cottagers' disappointing start to the season and Saturday's 3-0 defeat at West Ham proved to be the final straw for chairman Shahid Khan.
"Today I spoke with Martin to thank him for his efforts on behalf of Fulham Football Club over the past three seasons and, in particular, since my becoming Chairman earlier this year," Khan said.
"Martin was very gracious and I appreciate his understanding of the situation. There is no question Martin is an excellent football man and he has my utmost respect for the commitment he made to our club.
"However, our poor form and results this season are undeniable, and Fulham supporters deserve better. With more than half the season still ahead, an immediate change was necessary."
Former Spurs boss Jol, 57, took charge at Craven Cottage in June 2011 but Fulham have managed to win only three of their 13 Premier League games this season and the loss at West Ham was their sixth successive defeat in all competitions.
"It was a privilege to manage Fulham, one of the great clubs in the Premier League or anywhere in the world," Jol said.
"I am disappointed in this season but know there are better days ahead for Fulham and its supporters. I will always treasure my experience here and want to thank Mr Khan and everyone at Fulham for the opportunity."
Dutchman Meulensteen, 49, was appointed as Fulham's head coach on November 13 after working at Manchester United alongside Sir Alex Ferguson between 2007 and last summer.
"Rene Meulensteen was brought to Fulham to assist Martin and today was offered the challenge and opportunity to step in for Martin," Khan said.
"I thank Rene for accepting and now we move forward. I have great confidence in Rene and high expectations for our squad to respond."
Meulensteen, who takes over a team 18th in the Premier League ahead of Wednesday's home game against Tottenham, said: "I appreciate the faith Mr. Khan has put in me and will do my very best to honour his trust.
"We aim to get Fulham back on track, starting Wednesday night."