Hoon -- whose job is on the line for his role in the worst crisis of Blair's six-year premiership -- said on Wednesday that to avoid allegations of a cover-up, he overruled advice to shield the respected scientist from the spotlight.
Widely seen as a potential government "fall guy", Hoon is the most senior official to take the stand at the inquiry into the suicide of weapons expert David Kelly. Blair is due to testify on Thursday.
Hoon told the inquiry he believed that shielding Kelly from the limelight was not an option after the scientist admitted briefing a BBC reporter on a dossier on Iraqi weapons. The reporter later reported that the dossier had been “sexed up” to justify the invasion.
"I was certainly aware that the prime minister took essentially the same view that I did," he told the inquiry, citing a message from Blair's chief of staff.
"I accept ultimately this was my decision," he added. "I am not in any way trying to avoid that."
The inquiry has raised particularly awkward questions for Hoon, leading some commentators to suggest he could become its most high-profile casualty.
Hoon overruled advice from his most senior civil servant to protect Kelly from the foreign affairs committee. Having approved the scientist's appearance, he then contacted the committee chairman to curb the scope of questioning.
The scientist was grilled by a parliamentary committee on 15 July over his unauthorised meeting with a BBC journalist. Two days after the occasionally hostile questioning, Kelly committed suicide by slashing his wrist in the woods near his home.
Kelly's death, and the failure after the invasion to find any weapons of mass destruction to back up warnings in the dossier, have sent Blair's ratings plummeting.
A poll in the Sunday Telegraph showed 67% of those questioned thought his government had deceived the public.
Blair's top intelligence adviser John Scarlett stepped out of the shadows earlier to defend the dossier and reject claims that the government inflated intelligence on Baghdad's weapons.
But the inquiry has shown that a number of Blair aides pushed for the dossier to be hardened up in the days before its publication.