The news is both a surprise and a further fillip for Mr Clinton as he completes preparations for the one great set-piece of the campaign in which he is guaranteed to shine, and which almost certainly will lift him - however briefly - to the top of the polls.
Relations between the two have never been easy. For weeks it had sounded as if the New York Governor would barely grace the convention with his presence. The word from the Clinton campaign headquarters in Little Rock was that Mr Cuomo had refused to play a prominent role in Madison Square Garden. From Albany came the retort that no invitation had reached the governor's office.
True, wishful thinking persisted this spring that despite every sign to the contrary, the man who is still arguably the most famous Democrat might be under consideration as Mr Clinton's running mate: Mr Clinton, however, in what appeared damnation by faint praise, recently suggested that Mr Cuomo would make an admirable Justice of the Supreme Court.
Now, though, he is returning to the role at which he excels - electrifying his party before the battle with the sheer power of his language. In 1984, the Cuomo keynote speech stole Walter Mondale's convention show in San Francisco. Four years later, ironically, Mr Clinton's nominating speech for Michael Dukakis was judged one of the biggest flops of his political career.
The snaring of Mr Cuomo, and all it means for the appearance of party unity, is but the latest piece of good news for Mr Clinton. Suddenly, things are going as right for the Democratic candidate as they are going amiss for his two rivals. A disjointed Bush campaign was targeting the Clinton economic programme when Thursday's large and unexpected rise in unemployment was announced.
Meanwhile Ross Perot's honeymoon wears daily thinner. The latest allegations include charges that he offered a Clinton marketing consultant dollars 600,000 ( pounds 330,000) to switch allegiance, and a report in Time magazine that in 1986 he had part of a Bermuda coral reef blown up without a permit to enable his yacht to dock at his holiday home.
Mr Clinton's impending choice of vice-presidential candidate should ensure him a further spate of positive headlines. A decision is likely this week, with speculation focused on either Congressman Lee Hamilton of Indiana, or Senator Albert Gore of Tennessee, 44, an unsuccessful contender for the Democratic nomination in 1988.