He was also part of the team that faced the wrath of the British High Commission in Nairobi as they tried to court the East by cancelling lucrative tenders that had been given to London.
He would occasionally clash with High Commissioner Edward Clay, he of the "they-are-vomiting-on-our-shoes" fame, and for a reason.
A few days after Kibaki left Nairobi Hospital, where he was being treated early in his presidency, then-British minister for Africa, Baroness Valerie Amos, visited.
She announced that the United Kingdom would resume full aid to Kenya once talks between Nairobi and international financial institutions were finalised.
But Mwiraria, perhaps not willing to take dictation from London, met President Kibaki on March 14 with newly appointed Central Bank governor Andrew Mullei.
That evening, they cancelled a 10-year multibillion-shilling currency printing tender unilaterally awarded to British company Thomas De la Rue by previous CBK governor Nahashon Nyaga.
Mwiraria never survived the subsequent political witch-hunt, and some quarters still believe this was the genesis of his fall.
Others blame Mwiraria’s battles with Githongo, together with Cabinet ministers Kiraitu Murungi and Chris Murungaru, for his downfall.
Githongo had, apparently, said in his famous dossier that Mwiraria had said that “Anura Pereira is a strong supporter of President Kibaki”.
Pereira was the mastermind of the Anglo Leasing projects and had set up several shadowy companies, and Mwiraria painfully protested.
Mwiraria also told Parliament that at no time did he tell Githongo that Nairobi businessman Jimmy Wanjigi wanted to kill the anti-graft czar.
“He chose to smear my name and that of the President,” said Mwiraria.
“It is not my nature to talk loosely. (He also pulled) another surprise that, during a workshop in Mombasa, I once told him that Mr Wanjigi was planning to kill him. Another untruth.”
It was his final statement that, perhaps, marks the nature of Mwiraria: “I open up myself to investigations. I did my best at the helm of the Ministry of Finance. Any mistakes I may have made were purely human; and for those, I apologise to this House and Kenyans.”
But he was unable to attend to the subsequent fraud case due to ill health.