Talking exclusively to the Sunday Herald, he urged Glasgow to plan ahead for a possible Yes vote so that the city could capitalise on any benefits, including the thousands of jobs which could be created by new government departments.
He said that if Scots did back separation from the UK, Edinburgh should not automatically reap all the benefits of more public sector work. Glasgow and other cities needed to develop plans now to make sure they did not miss a trick, Purcell added.
"It is imperative that our leaders, both in local government and in the business community in Glasgow, plan for the hypothetical situation of an independent Scotland," he said.
Purcell said Glasgow already had a number of public agencies which could bring key parts of the machinery of government to the city under independence.
For example, the jobs agency Scottish Enterprise could be the nucleus of a Department of Business, the new police service and other justice agencies could secure a Scottish Home Office for the city, and Glasgow's print and broadcast industries could make the city the base for a new Department of Culture and Media.
Even without independence, he said greater powers for Holyrood would make such departments possible, and the city should think about them long term.
Purcell, once tipped as a Labour First Minister, stressed he was not advocating a Yes vote. He also declined to say how he would vote in the referendum next year, and said he had no "current" plans to return to politics.
He said: "The one great thing about being a private citizen these days is that there is no obligation to publicise how I will vote."
Purcell, 40, left office in March 2010 after almost five years as council leader when a drink problem spiralled into a nervous breakdown. He subsequently confessed to using cocaine while in office, and being warned by police officers that he might be blackmailed as a result.
Since leaving the limelight, he has spent the past three years recuperating and rebuilding his personal life, as well as developing a business consultancy and appearing at charity dinners.
Contacted by the Sunday Herald as part of a special report into independence and local government, Purcell agreed to speak because he said the subject was both dear to his heart and a pressing issue for his home city.
He said: "I was genuinely very ill for the first two years after my departure, and in the last year have managed to rebuild my personal life and a role within the business community in Glasgow.
"As I'm increasingly asked for these views by those that I work with in the private sector, it seemed timely to share my thoughts now."
He went on: "Whilst no longer in a role in local government or politics – and despite having no current plans to return – I am however still a proud Glaswegian, and as both a resident and as someone who works with significant companies in the private sector now, I have a huge interest in what the future holds for Scotland's largest city, whatever the outcome of the referendum.
"It is clear to me that regardless of the outcome, more powers will come to the Scottish Parliament over the next few years. I know for a fact there is at least one other city which is looking very discreetly at what opportunities an independent Scotland, or a Scottish Parliament enhanced with more powers and responsibilities, would create for them. I hope Glasgow is doing the same."
The city's current Labour leader, Gordon Matheson, who succeeded Purcell, has so far been wholly negative in his approach to independence. In October, he told the House of Lords select committee on economic affairs the debate had created a "climate of fear" among businesses, and he dreaded the impact of a Yes vote on defence, tourism and financial services jobs.
"Overwhelmingly, I am convinced that it would be wrong for Glasgow," he said.
But Purcell said the city had to be ready for both outcomes, regardless of political preferences, and there was no point just throwing your hands in the air if the country chose independence. Better to have a contingency plan ready, he said.
"For instance, you have Scottish Enterprise and Skills Development Scotland and a very effective business team at Glasgow City Council already in the city, that could form the basis of a future Department of Business and Innovation.
"The concentration of the new police service, Disclosure Scotland, Inspectorate of Prosecution and the Passport Office hypothetically would form the basis for a Home Office in the city.
"And with Glasgow being the settled home of broadcast and print media, and of course the beating heart of the creative industries of Scotland, where else would you base – in either a devolved or independent Scotland – a new and more ambitious Department of Media and Culture?
"Moreover, these organisations don't just secure jobs within themselves, they also secure jobs with those in the private sector that they work with and depend upon for supplies and the like."
He said that, whether the referendum resulted in a Yes or a No, ambitious long-term planning was needed now, during the austerity years, to seize opportunities when the economy finally revived.
He said: "While it's important that the city plays a full role in the debate, Glasgow must, absolutely must, be taking a long-term view.
"There is so much to be positive about in this debate about Scotland's future that it would be a lost opportunity to simply polarise the debate into a simple Yes or No."
Purcell's intervention in the independence debate comes at an awkward time for his successor. Matheson, who replaced Purcell in a bitter and divisive contest, is widely seen as a weaker leader than his old boss and a pawn of the national Labour Party rather than his own man.
His reputation peaked last May when Labour held on to the City Chambers despite a strong SNP challenge in the council elections.
However, Matheson's star has dimmed ever since. In December, he was reported to the procurator-fiscal after police caught him performing an alleged sex act with another man in a car.
Matheson subsequently apologised to his partner, Stephen Wallace, for "an affair".
The fiscal's office said there was insufficient evidence of a crime to prosecute.
Matheson generated more bad headlines last month when he dramatically scrapped a £15 million overhaul of the city's George Square after a panel of judges rejected his favourite design. The farrago cost taxpayers around £100,000. Asked if Matheson was doing a good job, Purcell, who is still a Labour Party member, responded: "Yes, he is – and it's clear from the fantastic election result that Team Labour, led by Gordon Matheson, achieved last year that the voters think so too."
However, Purcell's comments are bound to cause ripples at the City Chambers, where Matheson's critics are already pondering whether he is weak enough to oust from his leadership position at the Labour group AGM in May.