During a referendum campaign visit to Glasgow yesterday, Mr Cameron 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 Liberal Democrats, attempts to make a more positive case for a No vote.
However, his devolution pledge was dismissed by First Minister Alex 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 that is popular with voters, according to polls - if he returns to power after next year's General Election.
He cited his record on delivering the new Scotland Act, which from 2016 will make Holyrood responsible for raising about half of 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 Conservative 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 LibDems 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 on 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 day of a two-day campaign trip to Scotland.
Aides insisted he would be meeting "real people" during his stay after criticism of highly controlled previous appearances north of the Border when, for example, he toured an oil rig and went aboard a nuclear submarine.
Yesterday he met some of the servicemen who will be involved in providing security at the Commonwealth Games.
He also chatted with a group of youngsters from a nearby nursery who happened to be peering through the gates of the barracks.
Mr Cameron backed Alistair Darling's leadership of Better Together and praised campaign speeches by former prime minister Gordon Brown.
He insisted the campaign was putting a positive case for Scotland staying in the UK but stressed it would be "a dereliction of a politician's duty" not to challenge Mr Salmond's independence proposals.
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 also repeated his call for a live TV showdown with Mr Cameron, adding: "The Prime Minister is perfectly entitled to come to Scotland, and we are perfectly entitled to ask why he isn't prepared to have a debate in Scotland."