The politics of it all is incredible, given the hostilities (another understatement) between Mandelson and Brown during the last days of Labour in opposition and the first years in government.
However, for a business audience what is more important is what kind of business secretary will the soon to be Lord Mandelson make?
Mandy's enemies, and they are many an numerous inside his own party, will say that whatever his skills and experience, he is such a divisive figure that he will not be able to be an effective minister.
But those who take such a view will be letting their prejudice interfere with their judgement.
For Mandelson actually does have considerable experience in the area of business which should help the UK government chart a safe course through the economic storms ahead.
He is, first, a former Secretary of State for Trade and Indus
try, a job in which civil servants have told me he was a capable and thoughtful minister.
One example - he raised the idea of easing the bankruptcy laws to allow companies and individuals who fail to have a second chance.
He was also Northern Ireland Secretary, a post in which he was not liked by the Republicans, but in which he learned the value of diplomacy whilst also being tough when he needed to be. Also vital in dealing with business
After his double downfalls, his good friend Tony Blair made him Britain's European Commissioner where he has had the difficult and demanding role of responsibility for Trade.
In this capacity he managed to offend Nicholas Sarkosy, the French President, because of his tough stand against the subsidies the EU continues to pay to farmers, many of them French.
Most business people who see Mandelson's stand as the right one, seeking to reduced subsidies in the developed world whilst promoting more free trade which would allow developing countries to compete in agriculture on a level playing field.
What is known and the Doha round of trade talks - an attempt to free up world markets and end protectionism in Europe and America in particular - failed in the end.
His opponents blaming Mandelson, but his stance was consistently anti-protectionism, again a sign that he is business friendly.
Mandelson is archetypal new Labour. Indeed he is one of the architects of new Labour.
As such he is no great friend of the unions - becoming increasingly powerful within Labour again as the cash from big business donors dries up.
He is far more likely to take the side of business in internal debates within the UK government.
If the UK, as seems likely, is heading into a recession proper, business will want someone at the heart of the Whitehall machine fighting its corner.
Given that Brown has gone out of his way to end the political enmity between them, Mandelson will be in a strong position to influence government policy in favour of business.
Provided, that is, there is not a third fall from grace.
The reaction to the appointment seems to prove the thesis that business welcome Mandelson, whilst unions are not so sure.
Several union officials asked for their reaction today said they "too shocked" to comment. Their silence and alleged shock speaks volumes.
At least the Communication Workers Union had something to communicate.
It said Mr Mandelson was an experienced politician who had steered through legislation on the postal industry during his previous time at the Trade and Industry Department (DTI).
And Business groups widely welcomed the news that Mr Mandelson will replace John Hutton.
Just some of the comments:
John Cridland, deputy director-general of the CBI, said: "John Hutton has succeeded in giving the new Department for Business a sense of mission and drive that was lacking at its predecessor, the DTI. In particular, he has taken decisive action to try to deliver energy security of supply in the future.
"The Department for Business must have a heavyweight political big hitter at the Cabinet table, and we are encouraged that Peter Mandelson is returning to this role."
John Wright, chairman of the Federation of Small Businesses, said: "This shock return is no surprise to us, given Mr Mandelson’s previous tenure at the DTI and his current position as Britain’s European Commissioner for Trade.
"Mr Mandelson’s experience will mean that he can do away with the probationary period and get straight into the business of dealing with the current credit crunch.
"We will be seeking an early meeting with him in order to convey some very easy-to-implement measures to safeguard the future of small businesses during these difficult times."
David Frost, director general of the British Chambers of Commerce, said: "Peter Mandelson did a good job at the DTI and clearly understands business.
"His work in Europe and involvement in global trade discussions also mean that he knows where the UK fits within the international context. We look forward to working with him in these challenging economic times."
Interesting times indeed.
