Chief Secretary to the Treasury Ms Truss has defended Mr Johnson and put him forward as a candidate who deserves to lead the country.
Ms Truss attempted to bat away a string of criticisms about how he may not be a fit and proper person to hold office.
When the accusation that Mr Johnson was “the worst foreign secretary in living memory” was put to her by the BBC Radio 4 Today programme, she said such attacks were due to his “huge public appeal”.
She said: “I think it’s a sign – that he is being attacked shows the huge public appeal he has, the huge power he has to communicate.
“His record is of being the most successful mayor of London we have had, of being an excellent foreign secretary who got countries around the world to take action against Russia by expelling their diplomats.”
Sir Alan Duncan, Mr Johnson’s number two at the Foreign Office, has told how being his “pooper scooper” was “a full-time activity”, but Ms Truss claimed those were the comments of someone who does not “like Boris Johnson” and who does not want the Conservative Party to change.
Ms Truss’ comments come as Mr Johnson is set to unveil his leadership agenda today.
The former foreign secretary is expected to use his leadership launch to again insist Britain must quit the EU by October 31.
Ms Truss also denied Mr Johnson is to blame for the continuing imprisonment in Iran of British mother Nazanin Zaghari-Ratcliffe because he had suggested she was training journalists.
Ms Truss said: “I think this is a complete misplacement of blame.
“The people who are keeping Nazanin Zaghari-Ratcliffe in jail are the Iranians.
“This is an oppressive Iranian regime – I think it’s apologists for that regime who are putting the blame on Boris Johnson…
“The fact is he did a brilliant job in my opinion as foreign secretary… and in the case that you’ve just mentioned, it’s the Iranian regime who have held this innocent women in jail – let’s put the blame where it is really deserved.”
Ms Truss also defended Mr Johnson when asked about his sacking for “lying in public” about an affair, saying: “I do not think the British public is interested in Boris’s personal life.”
Defending the Tory leadership hopeful from accusations that he is refusing to speak to journalists during his campaign for the top job, she said: “He has got nothing to hide.
“This is the parliamentary stage of the process. The important thing is he is talking to parliamentary colleagues.”
Additional reporting by Press Association