Charles Kennedy died of a 'major haemorrhage' caused by his alcohol addiction
He was 55.
His family confirmed the results of a postmortem in a statement: "We are grateful to the many friends and also medical experts who sought to help down the years, but ultimately this was an illness Charles could not conquer despite all the efforts he and others made.
"We can now proceed to make arrangements for his funeral, and we will make an announcement on the details in due course."
Kennedy first became an MP in 1983. He took over from Paddy Ashdown to lead the Lib Dems from 1999 to 2006. In January 2006, however, he publicly revealed that he was receiving treatment for an alcohol problem and resigned as leader.
In 2006, he said in a statement:
I chose not to acknowledge it publicly before in this way because, if at all possible, I wanted to overcome it privately.
I learned the hard way of the need to face up to this medical problem, one that is dealt with successfully by many others on a daily basis.
In 2010 he was reelected to parliament. He was active in this year's General Election but lost his seat in the Ross, Skye, and Lochaber constituency in May.