The Liberal Democrat leader told the spring conference in Cardiff that the agreement on electoral reform and devolution would give the party's policies a voice over the next five years.
In a wide-ranging speech which attacked both Labour and the Tories for "can't-be-done" politics, Mr Ashdown hinted that the talks which ended last week would safeguard the Liberal Democrats' place in the history of the late 20th century.
Giving the Scots and Welsh more say via their own assemblies and people across the United Kingdom more power in their communities, was part of the party's "historic mission".
"We have, through choice, been able to work and agree with the Labour Party in this one crucial area - despite our different values, our different policies, our different philosophies and our different beliefs.
"Now that may be criticised by some. But it will be a great source of hope for millions in Britain who despair of politicians ever working together for the good of the country," he said.
There had been complaints from some Welsh Liberal Democrats that the party's new entente with Labour would make their jobs more difficult on the doorsteps. Floating voters in marginal seats would be tempted to argue that they might as well vote Labour if the two parties appeared close, they said.
Dai Davies, prospective candidate for Ceredigion, had accused the leadership of going "hand in hand" with Labour.
Mr Ashdown also used his speech to spell out in more detail his party's policy of putting an extra penny on income tax for education. The plan would cost the average family only 45p per week, he said, but would raise a substantial sum for every school.
A typical primary school with 250 pupils would gain pounds 16,000 per year, while a secondary school with 1,000 pupils would gain pounds 110,000. Every child born in 1997 would be entitled to a nursery place by 2000, and by the end of the next parliament, no child under 11 would be in a class of more than 30.
"If you don't think giving these children that chance is worth an extra 45p a week, then it's simple. Don't vote for us," he said. "Our politics is dominated by fatalism and timidity - by the idea that the British people are a bunch of mean-minded misery-cuts, as obsessed with tax as politicians and the press. Well, we say they're not. It's time we stopped treating them like children."
A spokesman for Mr Ashdown brushed aside suggestions made in a Sunday newspaper that he was trying to "hush up" the imminent birth of his first grandchild. He said Mr Ashdown was delighted that his daughter Katie, 31, who lives in France, was expecting a baby soon after the election.
Far from worrying about what becoming a grandfather would do to the 57- year-old politician's status as an "action man," he was "looking forward to being able to say, `we are a grandfather'," the spokesman said.Reuse content