Cllr Stephen Flannery, who has represented Southwark's Riverside ward since 2002, died in St Thomas' Hospital on Monday, aged 35.
Cllr Stephen Flannery
The spokesperson added "Despite the best efforts of the excellent staff at St Thomas' Hospital, Stephen finally lost his fight for life on Monday 20 February."
Cllr Flannery was elected as Lib Dem councillor for Riverside ward in the 2002 elections and was appointed executive member for housing in February last year.
His Riverside ward co-councillor and leader of Southwark Council Nick Stanton said: "Stephen made a huge contribution not only as a ward member but in his role as executive member for housing during the past 12 months.
"Stephen was a trusted friend and colleague and will be sorely missed by his executive colleagues, members and officers of the council as well as those he represented in the community."
Cllr Flannery had five years' experience of senior management and had been chair of Southwark Council's housing scrutiny sub-committee panel for nine months before he was appointed to the executive.
His partner, Guy, and his family wish to thank all friends and colleagues who have supported Stephen over the past months and for the many expressions of sympathy already received.
• In 2004 Cllr Flannery took part in I'm a councillor, get me out of here.