Dominic Raab dismissed repeated warnings astir his behaviour, a retired elder civilian servant who worked with him successful the Foreign Office has said.
Lord McDonald described his erstwhile brag arsenic a "tough taskmaster" whose methods did not assistance him execute his aims.
He told the BBC helium raised this with Mr Raab much than erstwhile but helium "disputed" it and was unwilling to listen.
The erstwhile lawman PM, who resigned connected Friday aft a bullying inquiry, apologised if helium upset anyone.
The enquiry recovered helium was "intimidating" and "aggressive" towards officials, but Mr Raab said his behaviour was not bullying, and that astir each of the complaints against him were dismissed.
It looked astatine 8 ceremonial complaints astir Mr Raab's behaviour during his erstwhile stints arsenic justness secretary, overseas caput and Brexit secretary.
Senior lawyer Adam Tolley KC, who led the inquiry, concluded Mr Raab's behaviour progressive "an maltreatment oregon misuse of power", and that helium "acted successful a mode which was intimidating" and "persistently aggressive" towards officials.
Lord McDonald, who worked arsenic Mr Raab's imperishable caput successful the Foreign Office, told BBC Radio 4's Today Programme: "I witnessed a pugnacious taskmaster. I witnessed a curate who knew what helium wanted to do.
"Frankly, I witnessed idiosyncratic whose methods did not assistance him execute what helium wanted to bash and that I raised with him much than once."
Asked if Mr Raab had listened, helium replied: "No, helium disputed it, helium disputed helium characterisation."
Lord McDonald said helium had not utilized the connection bullying to Mr Raab, partially due to the fact that things had not reached that signifier astatine the time.
"I was trying to get my brag to spot however his behaviour was making his nonrecreational beingness much difficult. I was trying to assistance him get the champion retired of his squad and I felt saying bullying would person been excessively aggressive," helium said.
Lord McDonald was not astatine the Foreign Office astatine the clip of the incidents which were complained astir and upheld by the inquiry.
After helium resigned, Mr Raab said a "very tiny number of precise activistic civilian servants" were efficaciously trying to artifact reforms they did not like, related to areas including Brexit, captive parole and quality rights.
"That's not on. That's not democratic," the MP for Esher and Walton said.
But Lord McDonald denied determination was immoderate civilian work activism, passive aggression oregon a abstracted civilian work agenda.
He added: "I saw nary grounds of a tiny radical of activists trying to undermine a minister. The contented is simply a minister's behaviour."
The FDA union, which represents civilian servants, has accused Mr Raab of peddling "dangerous conspiracy theories that undermine the impartiality and integrity of the civilian service" to "deflect from an autarkic investigation's disapproval of his conduct".
But Conservative adjacent Lord Marland said Mr Raab's resignation was "almost a conspiracy by the civilian service".
Speaking to the BBC's Newsnight, helium said it was "a precise achromatic time for each employers" due to the fact that a "dangerous precedent has been set" [on the contented of workplace bullying] that would "send shudders done each employers successful the country".