Sir Menzies Campbell has warmly remembered the former Liberal Democrat leader as a "gregarious" man who "enjoyed a good gossip".
Speaking to ITV News, Campbell spoke how in 2003 Kennedy made a huge impact in politics when he steadfastly denounced the march to war against Iraq.
Not long after the invasion, Kennedy and Campbell met the-then US President George Bush who was in the UK on a state visit.
"We went into the room in Buckingham Palace expecting their might be a bit of trouble," Campbell recalled.
MPs will have the chance to pay tribute to Charles Kennedy in the House of Commons tomorrow.
Speaker John Bercow said there would be a dedicated session timetabled after Prime Minister's Questions.
Announcing Kennedy's passing to parliament, he said: "It is with deep sadness that I must report to the House the death of the former member for Ross, Skye and Lochaber Charles Kennedy.
"He represented his constituency in its various forms for almost 32 years.
"It is, moreover, a matter of record that he led his party, the Liberal Democrats, from 1999 to 2006 achieving the best parliamentary representation of his party in this House in living memory."
Former prime minister Gordon Brown has admitted he tried to get Charles Kennedy to join Labour at the start of his career.
Paying tribute to Kennedy, who died yesterday aged 55, he said: "The first time I met Charles in 1983 - we entered parliament from Scotland at the same time - I had recognised his ability and asked him to join the Labour Party.
"He politely declined. The last time I was in touch with him was to pass on condolences when his father, with whom he remained very close, sadly died just before the 2015 election."
Brown said Kennedy was "one of the greatest debaters, orators and communicators who brought humour to politics".
"Possessing the warmest and most engaging of Scottish highland personalities, coupled with a natural charm that made him popular among even those who disagreed with him, he will be remembered as one of the most gifted and personable leaders of our time," he added.
Tony Blair, who Charles Kennedy took on almost singled-handedly over the war in Iraq, has called the death of the 55-year-old an "absolute tragedy".
The former prime minister said: "He [Charles] came into Parliament at the same time as me in 1983.
"He was throughout his time a lovely, genuine and deeply committed public servant.
"As leader of the Liberal Democrats, we worked closely together and he was always great company, with a lively and inventive mind. I am very saddened indeed by this news."
Scottish Labour leader Jim Murphy has said the greatest tribute he could pay to Charles Kennedy is "that I always wished he was Labour".
He added: "Charles was so talented and popular with the general public. He will be sadly missed across Scotland and the whole United Kingdom. Charles was a man I was proud to call a friend."
Paddy Ashdown has said the death of "unusual and increasingly rare figure" Charles Kennedy is a "terrible loss".
Speaking to ITV News, the former Lib Dem leader said it was a loss not just to the party but to the body of politics on a wider scale.
He said: "You think of his opposition to the Iraq war - but history has proved him right.
"You think of him in an age of manicured, perfectly presented politicians who are not liked in the country - his ability to reach out well beyond the circle of Westminster is one of the reasons why he is so loved.
"And you realise that a rather unusual and increasingly rare figure has been lost to us, and that is a very sad event."
Ed Miliband has described the death of Charles Kennedy as a "tragic loss".
The former Labour party leader, who resigned after his party's General Election defeat in May, tweeted: "Charles Kennedy was a principled, decent man. his death is a tragic loss. My heart goes out to his family."
Charles Kennedy was a principled, decent man who stood up for what he believed.His death is a tragic loss.My heart goes out to his family.
Alastair Campbell has spoken of being "saddened to the core" at the death of his "very good friend", Charles Kennedy.
In a highly personal blog on his website, the former Labour Party director of communications paid tribute to the "talented politician", one of the few outside of the Labour party with whom he enjoyed close relations.
Praising the former Liberal Democrat leader's political record and integrity, Campbell also spoke about how alcohol for good or ill played a part in their relationship and how they used a private code - "health remains fine" - as a sign that they weren't drinking.
Campbell was keen to present Kennedy's statesmanlike qualities, writing: "He was a terrific communicator and a fine orator. He spoke fluent human."
[Charles] was great company, sober or drinking. He had a fine political mind and a real commitment to public service. He was not bitter about his ousting as leader and nor, though he disagreed often with what his Party did in coalition with the Tories, did he ever wander down the rentaquote oppositionitis route. He was a man of real talent and real principle.
Nick Clegg said this was why it was so tragic to see someone with 'such huge gifts' struggle with demons - in Kennedy's case alcohol.Read the full story ›
David Cameron has described Charles Kennedy as a "talented politician who has died too young," following news of the 55-year-old's sudden death.