"I think it is a shambles and a disgrace," he said, in a video that a couple of other Conservative lawmakers tweeted in agreement.
"I have made a mistake, I accept responsibility, I resign," she said in a letter to the prime minister.
As a replacement, Truss appointed former minister Grant Shapps, who said recently that Truss faced a massive battle to survive.
He also failed to offer a ringing endorsement of the prime minister.
"I have been very clear that I am sorry, and I have made mistakes," Truss told jeering opposition lawmakers in parliament.