Lenin's Tomb has existed since June 2003 and was listed in 2005 as the 21st-most-popular blog in the country. Although run by Seymour, it also has front-page posts from other contributors, including, occasionally, China Mieville. It has been cited by the BBC, The Guardian, Private Eye, and Slate magazine. Seymour writes about "issues such as imperialism, Zionism, Islamophobia and anti-capitalism, and covers strikes and protests with footage, images and reportage".

Early reviews of Seymour's 2008 book, The Liberal Defense of Murder, included both praise and criticism. A review from the journalist Gary Younge that was featured on the book's cover maintains that the author "expertly" traces the descent of liberal supporters of war "from humanitarian intervention to blatant islamophobia". China Miéville praised the book as an "indispensable" guide to the "pre-history and modern reality of the so-called 'pro-war Left'". Owen Hatherley, writing in the New Statesman, praised the book as "a freshly written, heavily footnoted and clearly obsessively researched history of 400 years of the 'decent left'". An Independent on Sunday review described it as "an excellent antidote to the propagandists of the crisis of our times", and a later review in The Independent by the policy director of Save the Children described the book as "timely, provocative and thought-provoking".

A review in The Times praised the book as a "powerful counter-blast against the monstrous regiment of 'useful idiots'" who have "contributed in recent decades to the murderous mess of modern times". On the other hand, Oliver Kamm, writing in The Times blog, disputed the review, accusing the author of some historiographical distortions and spelling mistakes. Seymour posted a lengthy reply to Kamm's criticisms on his own blog, Lenin's Tomb.

A critical review in The Guardian by Philippe Sands contended that despite the book's "damning material" on the supporters of war, this "potentially important book" was weakened by "the generality" of its conclusions and the failure to concede that there are instances where the use of force is justified. Seymour also responded to this critique on his weblog. An enthusiastic review appeared in Resurgence magazine in March 2010, declaiming that: "Richard Seymour's obsessively researched, impressive first book holds its place as the most authoritative historical analysis of its kind". A scholarly review in the Journal of American Studies commended the book's "truly impressive breadth and depth", arguing that it provided "a new European perspective — and a warning — on the left’s pragmatic and ultimately shortsighted support for imperialist adventures".

Seymour was interviewed about the book's contents on Doug Henwood's Behind The News radio show on 27 November 2008. A later interview on the literary website, ReadySteadyBook, discussed Seymour's motivations in writing the book, and his responses to critics. He explained that: "The shape the book eventually took, as a genealogy of liberal imperialism, was prompted by the combat clerisy themselves. They were the ones appealing to the legacy of 19th Century liberal imperialism. They were the ones vaunting a kitschy manifest-destinarianism, as well as a muscular determination to visit vengeance on the barbarians. It was they who culled their catchphrases from a disgraced imperial lexicon. Unless I wanted to write a gossipy, huffy polemic in the manner of Nick Cohen's What's Left, I had no choice but to anatomise these discursive strategies from their origins to the present day."