It comes following their 2-1 home defeat to Newcastle on Tuesday, which left the cub struggling in 16th position in the Premier League.
The club sit just five points above the relegation zone after just two wins in 17 league matches.
Frank faced calls to be "sacked in the morning" by angry supporters during the defeat to Newcastle, which were followed by chants for old boss Mauricio Pochettino to be appointed.
It is understood the club's hierarchy made the decision to dismiss the 52-year-old following the game, with 12 days until they host bitter rivals Arsenal.
In a statement, they said: "The Club has taken the decision to make a change in the Menâs Head Coach position and Thomas Frank will leave today.
"Thomas was appointed in June 2025, and we have been determined to give him the time and support needed to build for the future together.
"However, results and performances have led the Board to conclude that a change at this point in the season is necessary.
"Throughout his time at the Club, Thomas has conducted himself with unwavering commitment, giving everything in his efforts to move the Club forward. We would like to thank him for his contribution and wish him every success in the future."
The Dane joined the club from Brentford in July, replacing Ange Postecoglou who was sacked after finishing in 17th place, but also winning the Europa League.
His future was considered after last monthâs 2-1 home defeat to West Ham, but it was decided he would be given more time given the hectic fixture schedule and the lack of alternatives available.
But following Januaryâs FA Cup exit to Aston Villa, the squad are now without a game this weekend and have the chance of a reset with Frankâs tenure concluded after only 13 wins in 38 matches.
More to follow...