Article published on the 2010-01-12 Latest update 2010-01-12 15:19 TU
Campbell was one of the ex-prime minister's closest allies and his former director of communications and strategy.
He told the inquiry that Blair wanted to pursue a diplomatic route right up to a crucial vote on the Iraq war in the House of Commons in March, 2003.
"I think the prime minister was all the way through tryng to get it resolved without a single shot being fired," he said.
US-led forces, supported by Britain, began their invasion of Iraq two days after the House of Commons vote without explicit backing from the UN Security Council.
Campbell is the first big name witness to appear before the inquiry led by retired civil servant John Chilcot.
Blair himself will appear at the end of the month.
Meanwhile in The Hague today, an entirely separate Dutch Independent Commission probing support from the Netherlands for the invasion of Iraq made ITS report public today.
The commission concluded that there was insufficient legitimacy for the invasion.