Argent was one of a number of the reality TV programme's stars to hit the roads of the capital this morning (April 22), in order to raise money for a variety of good causes.
Following completion of the 26.2-mile course, Argent posted a picture of himself holding his participant's medal, captioned: "6 weeks ago I was 18 stone and couldn't run down my road. Just completed London Marathon #LookAtMeNow (sic)"
He continued: "Received so much stick n lots believed I wouldnt do it but proved those Haters/Doubters wrong! Hope Granddad Seamus is proud! #CancerResearch."
The Essex celebrity, who has raised a total of £3,313 for Cancer Research UK, added: "As @justinbieber says #NeverSayNever #VirginLondonMarathon2012 #CancerResearch @carakilbey @BilliMucklow NEVER FORGET! Lifetime Achievement!x"
According to the Daily Mail, Argent completed the course in 06:01:01, while his TOWIE cast mates Cara Kilbey finished in 05:47:45 and Billi Mucklow came in at 06:02:37.
Prince Harry presented trophies to the winners of today's race and joked that Prince William and Kate Middleton will participate in the race next year.
Watch the TOWIE cast's interview with Digital Spy below:
> TOWIE preview: Arg loses two stone, Lauren gets emotional - pictures