Thorn began his YouTube channel, Philosophy Tube, as an educational channel in 2013 in response to the university tuition fees tripling in the United Kingdom in 2012, rendering higher education less accessible. Thorn made it his mission statement to “[give] away a philosophy degree for free”. Thorn originally planned to record his lectures and upload them, rather than appearing in videos, but his university would not allow this. His first video titled “I think therefore I am” about René Descartes was uploaded in May 2013. As of October 2020, the channel has 752,000 subscribers and the videos’ cumulative view tally is 47 million. Thorn makes money from both YouTube advertisement revenue and crowdfunding on Patreon.

Born Oliver Lennard, Thorn is from Newcastle upon Tyne and has two older brothers. He attended the Royal Grammar School, where he was a member of an army cadets group. Taking Philosophy as an A-level alongside Biology and Chemistry, Thorn credits his discovery of the subject with his teacher. Thorn studied Philosophy and Theology at the University of St. Andrews, where he also participated in Mermaids and the St Andrews Revue. Thorn graduated with a first-class Scottish Master of Arts in Philosophy in 2015. He then trained at East 15 Acting School, completing a Master of Arts awarded by the University of Essex in 2017 before moving to London.

The channel’s style progressed over a period of years from a direct style of talking to the camera about the works of philosophers such as Descartes and Kant, to more theatrical productions. In 2016, Thorn took part in the YouTube NextUp, a week-long training programme for YouTubers with under 100,000 subscribers. Following attendance at the 2018 conference VidCon, Thorn decided to change his content creation, beginning to film at a studio with costumes and makeup. He also used props such as snakes and horses. Kayleigh Donaldson of Pajiba described Thorn’s recent works as “long-form think-pieces” with “detailed production design”, that use aspects of sketch comedy. Emily VanDerWerff of Vox summarised that the channel covers both philosophical topics and “sociopolitical ideas of the current era from a leftist point of view”. For instance, a video beginning with the subject of Brexit becomes a discussion more broadly about democracy. Another video about former Trump advisor and Breitbart News co-founder Steve Bannon features Thorn performing a cover of a Hadestown song, with lyrics about Bannon. VanDerWerff praised that Thorn “undercuts [Bannon’s] entire shtick”.

Thorn’s 2018 video “Suic!de and [email protected] [email protected]” discusses societal attitudes to mental health, along with his personal experiences: he has a history of self-harm and attempted suicide twice in his life. He said in mid-2019 that he still received at least one email per day by a person who said the video saved their life. Thorn’s video “Men. Abuse. Trauma.” is about men and mental health, with reference to his personal experiences. The video is 35 minutes long, with the script entirely memorised by Thorn. There are no cuts or editing, and a single costume change is facilitated by a slow camera pan across the room; Thorn used the second of two takes. Both the script and the style of the video reference the 1944 Jean-Paul Sartre play No Exit. Emily VanDerWerff of Vox praised that the “tension and vulnerability that builds” is maintained by the lack of editing, and opined that in the video, “aesthetic form is inseparable from content”.

In October 2019, Thorn discussed his sexuality in his YouTube video “Queer✨”, where he came out as bisexual and stressed his sexuality was trans-inclusive.

In July 2019, Thorn discussed his channel on the BBC radio show World Business Report.

In 2019, Thorn, with the help of producers Isabella O’Hammon and Alice Quinn Rose, started a charity stream in which he aimed to read the Complete Works of Shakespeare in order to raise money for the Samaritans, a UK charity that helps people in emotional distress. Thorn chose the charity because he said that its telephone hotline “saved my life when I was considering suicide”. He chose Shakespeare based on the idea that “Shakespeare features every human emotion”, which he attributed to Judi Dench. The stream was inspired by a January 2019 video game stream by hbomberguy which raised £278,000 ($340,000) for British charity Mermaids. It was announced at the end of his YouTube video “Men. Abuse. Trauma.”, which was released in late July 2019.

Thorn has written for publications such as HuffPost UK, The Independent, and Broadway Baby. He has done stand-up, voiceover work, and stage acting. In summer 2019, he played Claudio in the UK outdoor tour of Much Ado About Nothing.

In 2019, Dani Di Placido of Forbes praised that Thorn “doesn’t tell you what to believe, but he prompts his audience to ask themselves why they believe the things they do.” Shannon Strucci, writing for the magazine Sight & Sound published by the British Film Institute, said that Thorn’s videos “vary tremendously” in “tone and content”. Strucci described the videos as “always well-researched, inventive, and theatrical”. The German broadcaster Deutsche Welle praised the videos as entertaining and elaborate in design. Di Placido included Thorn on a list of “5 Fantastic YouTubers Fighting The Spread Of Alt-Right Propaganda”, whilst the channel Philosophy Tube was recommended in the Slovak broadsheet SME. The Irish author and broadcaster Emma Dabiri has enjoyed Thorn’s videos.