Symons was placed in temporary charge in mid-September after the dismissal of Felix Magath, with the club languishing at the bottom of the Championship following their relegation from the Premier League.
Since taking over from Magath, Symons has guided Fulham to four league victories and out of the bottom three.
Owner Shahid Khan is in no doubt that the 43-year-old is the right fit for Fulham, highlighting his passion for the club for whom he played between 1998 and 2001.
Khan told the club's official website: "Kit has thoroughly earned the opportunity to take Fulham from here as our first-team manager.
"We've been a different football club, on and off the pitch, since Kit stepped in as our caretaker manager in September.
"His passion for Fulham is evident and contagious, and I believe the promise ahead of him is extremely bright.
"Above all, Kit understands and is committed to our goals, and he knows there is much work ahead. Starting today, we can begin work with Kit firmly in charge at Fulham."
Symons - who has penned an 18-month deal - begins his full-time role with a trip to Wigan Athletic on Saturday.
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