Gordon Brown and his wife Sarah have had a baby boy, it has been announced.
The Browns called their first child an "inspiration"
A brief statement from the chancellor's spokesman confirmed the birth took place on Friday morning.
Both mother and baby are said to be "fine".
News of Mrs Brown's pregnancy appeared in March - just over a year after the couple's first child, Jennifer Jane, died when she was only 10 days old.
A spokesman for the chancellor said: "Sarah Brown gave birth today at 0928 BST to a baby boy at the New Royal Infirmary, Edinburgh.
"He weighed 8lb 1oz. Both mother and baby are doing fine.
"Sarah and Gordon have not yet decided on a name. They and their families are delighted."
Dr Rhona Hughes, consultant obstetrician at the hospital, said: "Mother and baby are both doing very well.
Born 20/02/51 in Glasgow
1983 becomes MP for Dunfermline East
1987 joins Labour's frontbench
1992 shadow chancellor
Blair appoints him chancellor after 1997 Labour victory
Marries PR executive Sarah Macaulay in 2000
"Sarah and Gordon are both delighted - it was a very emotional moment and they both wept tears of joy."
Prime Minister Tony Blair was one of the first to offer Mr and Mrs Brown his congratulations.
"This is wonderful news. Cherie and I are absolutely delighted," he said.
Tory leader Iain Duncan Smith said he was "overjoyed".
"Children are an immense blessing and I am sure their new son will bring great fulfilment to their lives," he said.
Mr Brown was present for the birth and it is understood that he will take paternity leave.
Both the chancellor and his wife have expressed their thanks to the staff at the hospital.
Harry Potter author JK Rowling, who has a home in Edinburgh, visited the Browns in hospital on Friday evening.
On leaving, she said the baby was "really, really
gorgeous" and the couple were both well.
John Brown said the couple were "in awe" of the new arrival
Mr Brown's elder brother John said: "The whole family are delighted at
the birth of Sarah and Gordon's baby. He is a beautiful boy."
Liberal Democrat leader Charles Kennedy said he was delighted for the Browns.
"I wish them both every happiness with their new son," he said.
Mr Brown's Conservative opposite number, Michael Howard, said: "I am delighted by the
news and wish Gordon, Sarah and the baby every joy."
Scotland's First Minister Jack McConnell said he and wife Bridget were "absolutely delighted" by the news.
"We wish them all the joy and happiness a family can bring," he said.
Jennifer Jane Brown was born in December 2001 at Forth Park Hospital in Fife seven weeks premature.
She died at the Royal Infirmary in Edinburgh a little more than a week later after suffering a brain haemorrhage.
At the time, Mr Brown, 52, said she had been an "inspiration" to both him and his wife, whose lives would not be the same again.
The chancellor and his wife, 38, who works under her maiden name of Sarah Macaulay, were married in August 2000 at a private ceremony in North Queensferry, Fife.
Ministerial births in Downing Street have become more commonplace, with Tony Blair in 2000 becoming the first prime minister in 150 years to father a child while in office.