The 61-year-old has paid the price for an abysmal start to the season in which Fulham have taken just one point from seven matches.
Magath arrived at Craven Cottage as a replacement for Rene Meulensteen in February but failed to keep the club in the Premier League.
Back in the second tier for the first time since the 2000-01 season, Fulham have struggled to adjust to life in their new surroundings and prop up the table following Wednesday's 5-3 loss to Nottingham Forest, which signalled the end of the German's tenure.
"This is an unfortunate but necessary change," said Fulham chairman Shahid Khan.
"I am doing what I feel is right and needed for Fulham football club, for today as well as tomorrow.
"I thank our supporters for standing by us during these most difficult of times on the pitch, and promise better days ahead."
Symons will now take charge for the home clash with Blackburn Rovers on Saturday.
