[3] Now living in England, Kumar is founder and Director of Programmes of the Schumacher College international center for ecological studies, and is Editor Emeritus of Resurgence & Ecologist magazine.

His most notable accomplishment is the completion, together with a companion, E. P. Menon, of a peace walk of over 8,000 miles in June 1962 for two and a half years, from New Delhi to Moscow, Paris, London, and Washington, D.C., the capitals of the world's earliest nuclear-armed countries.

[7] Inspired by Bertrand Russell's civil disobedience against the atomic bomb, in June 1962 Kumar and his friend E. P. Menon decided to dedicate themselves to undertaking a peace walk from India to the four capitals of the nuclear world, Moscow, Paris, London, and Washington D.C., and decided to carry no money on their trip.

Leaving Pakistan via the Khyber Pass, they continued through Afghanistan, Iran, Armenia, Georgia, and the Caucasus Mountains, reaching Moscow, then Paris, London, and Washington, D.C. Travelling on foot and carrying no money, Kumar and his companion would stay with anyone who offered them food or shelter.

Kumar was interviewed by Richard Dawkins in his 'Slaves to Superstition' episode of the documentary The Enemies of Reason, investigating the prevalence of unscientific beliefs in modern society.

It contains a collection of statements from tribal people, photographs, and essays from international authors, campaigners, politicians, philosophers, poets, artists, journalists, anthropologists, environmentalists and photojournalists.

[14] Prior to the 2015 UK general election, he was one of several celebrities who endorsed the parliamentary candidacy of the Green Party's Caroline Lucas.