87-year-old Lord Avebury, a renowned human rights campaigner, passed away in his house in Camberwell, south London, surrounded by his family, National Secular Society of which he was a member announced.
The politician was the longest-serving Liberal Democrat member of the House of Lords, taking his place in the upper chamber after losing his seat in the Commons in 1970.
He suffered from myelofibrosis, a form of blood cancer, for more than a year and had spoken publicly in support of assisted dying.
As Eric Lubbock he won the seismic Orpington by-election in 1962.
When he was defeated after eight years as an MP in Orpington he famously quipped, "In 1962 the wise, far-seeing people of Orpington elected me as their Member; in 1970 the fools threw me out".
Subsequently, as Lord Avebury he was a regular champion of international and human rights causes in the House of Lords.