The organisation faces a "fundamental threat" from email and must be reformed in order to survive, the senior Lib Dem insisted.
The performance is expected to encourage the Government to cash in on the turnaround by pressing ahead with a privatisation this year.
"The point is that it is not this particular government adopting an ideological position," Cable told BBC Radio 4 Today. "We are following in the footsteps of the last government that recognised that certain things had to happen in order for Royal Mail to survive because it is faced with a fundamental threat to its business from email."
Ahead of a possible stock market floatation, results for this year are more than double the £152 million profit in 2012.
Mr Cable said around 10% of shares should go to the work force.
"It isn't a bribe, but it gives them a stake in the ownership," he added.
Unions have warned that services will go into decline if the business is sold off.
Dave Ward, deputy general secretary of the Communication Workers Union (CWU), whose members will be balloted on the proposals this week, claimed loopholes would allow the universal service obligation to be eroded.
"There are opportunities for them to down dial the terms of the universal service in the future," he told BBC Radio 4's Today programme.
"People who live in the suburbs, people who live in rural areas, people who live in villages will not get the same service under a private company."
The National Federation of SubPostmasters (NFSP) said the plans for privatisation should be postponed to prevent an "even deeper crisis" for Britain's post offices.
It is concerned that a privatised Royal Mail would not feel obligated to keep services with the Post Office network.
Chief executive Moya Greene, who last year returned the core postal business to profitability after four successive years of losses, said it was a strong performance and that the transformation of Royal Mail was under way.
The core postal business, which delivers the six-days-a-week universal service to 29 million addresses, reported operating profits of £331 million and improved its margin from 0.5% to 3.9%.
Parcel deliveries now account for almost half of the group's revenues of £9.3 billion in the last year.