During a referendum campaign visit to Glasgow yesterday, the Prime Minister also insisted Scotland enjoys "more oomph" on the world stage as part of the UK.
His comments came as the pro-UK Better Together campaign, comprising Labour, the Conservatives and Lib Dems, attempts to make a more positive case for a No vote.
However his devolution pledge was dismissed by First Minister Salmond, who said: "Nobody will believe Tory promises of more powers for Scotland."
Mr Cameron aimed to reassure Scots that more powers would be transferred to Holyrood - a move which is popular with voters, according to polls - if he returns to power after next year's Westminster election.
He cited his record delivering the new Scotland Act, which from 2016 will make Holyrood responsible for raising about half the income tax Scots pay.
He also highlighted moves to give legislative powers to the Welsh Assembly and hand control of policing to Northern Ireland.
He said: "I think I have a track record of showing respect of the nations of the United Kingdom and achieving devolution so that our family of nations can stay together and find a settlement with which all are comfortable."
He added: "It's very important if you want further devolution, the way to get it is a No vote. A Yes vote is an end to devolution, it's the start of irreversible separation."
Mr Cameron declined to outline specific new powers for the Scottish parliament, saying he would not prejudge the conclusions of a party devolution commission headed by Lord Strathclyde.
The group is expected to recommend a further extension of Holyrood's income tax raising powers when it reports later this month.
Labour and the Lib Dems have already presented their plans to increase tax powers as part of wider devolution packages to be put to voters next year, if Scots reject independence.
However they have faced repeated SNP claims that extra powers are not guaranteed.
Speaking during a visit to a Royal Regiment of Scotland barracks in Maryhill, the Prime Minister also highlighted Britain's armed forces and influence in international bodies such as the EU, UK and G8 as reasons to reject independence.
He said: "I see at first-hand what Britain has together in terms of these resources that can keep us safe, and of course Scotland could have some of those things if it were independent, but think of what we have together and think of how much more oopmh that gives us in the world."
The visit came on the first of a two day campaign trip to Scotland.
Aides insisted he would be meeting "real people" during his stay following criticism of highly controlled previous appearances north of the Border when, for example, he toured an oil rig and went aboard a nuclear submarine.
Mr Salmond said: "Nobody will believe Tory promises of more powers for Scotland, because the last time that happened the only thing Scotland got was Thatcherism and 18 years of Tory governments we didn't vote for."
He repeated his call for a live TV showdown with Mr Cameron.