An "exceptionally happy" Charles Kennedy and his wife Sarah have left hospital with their new-born son.
Donald James is the couple's first child
Donald James was born in St Thomas' Hospital in London at 0014 BST and weighed six pounds, nine ounces.
Mrs Kennedy said she felt "fantastic" and said her husband had been a "real support" during the birth.
The Lib Dem leader said the new baby was a "pride and joy" and he would rejoin the election campaign later this week with a "spring in his step".
New clan member
The Lib Dems postponed their manifesto launch when Mrs Kennedy went into hospital on Monday.
As the couple left hospital, Mr Kennedy told reporters: "Everything went tremendously smoothly. We are very grateful and fortunate about that.
"And we are exceptionally happy with the new Donald James Kennedy that becomes the latest addition to the clan. I think he's our pride and joy."
He thanked his colleagues for covering for him in his absence from campaigning.
"We always knew this coincidence of circumstances could come about, although it was never planned that way.
"After we have a bit of a private break together, towards the end of the week I will be looking forward to rejoining the campaign but I will be joining it with a song in my heart, with a spring in my step."
He thanked the hospital staff for their fantastic support and family and friends for their messages and gifts.
Mrs Kennedy said she inevitably felt tired but added: "It was a good experience."
Tony Blair and Tory leader Michael Howard were quick to offer their congratulations to their colleague.
Labour leader Tony Blair said: "I just wish them well and we all wish them well. It is a particular joy when you have your first baby."
For the Tories, Michael Howard said: "It is wonderful news. I send them my warmest congratulations."
It has been reported that the baby is named after Mr Kennedy's grandfather Donald, to whom the leader was very close.
Deputy leader Sir Menzies Campbell has taken over Mr Kennedy's campaign duties while the Lib Dem leader stays with his wife and new son.
Mr Kennedy had been due to board a plane for Devon on Monday but was called back to London after his wife, 35, was admitted to hospital.
On Sunday, Mrs Kennedy appeared alongside her husband on the campaign trail for the first time.
The Liberal Democrats held a news conference about the economy on Tuesday in place of their manifesto launch and Sir Menzies took Mr Kennedy's place on a visit to Bristol.
Lib Dem campaign chief Lord Razzall told journalists: "We are all absolutely delighted and send our congratulations to Charles and to Sarah."
Lib Dem trade and industry spokesman Malcolm Bruce told BBC News: "It will do the campaign absolutely no harm.
"It's not just women - an awful lot of men like babies too and people generally respond warmly to family pictures.
"It makes a point that here is a man who has a new family and I think a lot of the issues we are addressing are about families in Britain today.
"We are happy for any family that has an event of this kind and it is just one of those fortuitous outcomes that Charles and Sarah have had a baby at the start of an election campaign."