Frank, who replaced Australia's Ange Postecoglou after his sacking last June, had been under mounting pressure at the north London club.
Tuesday's 2-1 home defeat by Newcastle left his team in 16th place with 29 points from 26 matches and looking over their shoulder at the relegation zone.
"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," Spurs said in a statement on Wednesday.
"However, results and performances have led the board to conclude that a change at this point in the season is necessary."
Frank, who joined Brentford in 2018 and established them as a top-flight club after gaining promotion, struggled to replicate those methods at last season's Europa League winners Tottenham.
The writing looked on the wall for the 52-year-old after Tuesday's loss to Newcastle - their 11th of the league campaign.
Supporters left no doubt about their feelings with jeers ringing out around the club's stadium and chants of "You're getting sacked in the morning" directed at Frank.
It was Tottenham's seventh EPL defeat at home this season and they have won only two of their 13 league games in front of their own fans.
