[2] The director of Index on Censorship, John Kampfner, said: "The Russian government's treatment of Luke Harding is petty and vindictive, and evidence – if more was needed – of the poor state of free expression in that country.

Lavrov also added that Harding had previously broken the rules of his press accreditation by visiting the area of counter-terrorism operations without informing the relevant security authorities.

Harding has said that during his time in Russia he was the subject of largely psychological harassment by the Federal Security Service, whom he alleges were unhappy at the stories he wrote.

[14] On 1 September 2011, it was revealed that an encrypted version of WikiLeaks' huge archive of un-redacted US State Department cables had been available via BitTorrent for months and that the decryption key had been published by Leigh and Harding in their book.

In 2016, Harding published A Very Expensive Poison, an account of the murder of the Russian ex-KGB whistle-blower and Putin critic Alexander Litvinenko.

[29] In November 2017, Harding published Collusion: Secret Meetings, Dirty Money, and How Russia Helped Donald Trump Win on the subject of Russian interference in the 2016 United States elections.

The book examines the dossier by former British spy Christopher Steele, and alleges that Trump was the subject of at least five years of "cultivation" by Soviet/Russian intelligence services prior to his election, and possibly by the KGB as soon as 1987.

[30][31] In May 2021, former The New York Times reporter Barry Meier published Spooked: The Trump Dossier, Black Cube, and the Rise of Private Spies, which cited the Steele dossier as a case study in how reporters can be manipulated by private intelligence sources; Meier named Harding and MSNBC's Rachel Maddow as examples.

[32] On 27 November 2018, Harding co-authored an anonymously sourced article for The Guardian claiming that Julian Assange and Paul Manafort met several times at the Ecuadorian embassy in 2013, 2015, and 2016 possibly in relation to the 2016 Democratic National Committee email leak.

[34] According to Glenn Greenwald citing Tommy Vietor, "if Paul Manafort visited Assange at the Embassy, there would be ample amounts of video and other photographic proof demonstrating that this happened.

According to David Bond, Harding's Shadow State also "raises fresh questions about the way the UK government has handled claims of Kremlin interference in Britain’s democratic processes.

"[38] In July 2021, Harding, Julian Borger, and Dan Sabbagh announced that The Guardian had received a document allegedly leaked from the Kremlin.

The document, said to have been produced on January 22, 2016, appears to authorize Putin's plan for Russian interference in the 2016 US election on behalf of "mentally unstable" Donald Trump.