He also co-hosted the comedy podcast The Bugle with Andy Zaltzman, with whom Oliver had previously worked on the radio series Political Animal and The Department.

The show's influence over US culture, legislation, and policymaking has been dubbed the "John Oliver effect", and he was included in the 2015 Time 100, where he was described as a "comedic agent of change [...] powerful because he isn't afraid to tackle important issues thoughtfully, without fear or apology".

[8][9][10] He was raised Anglican, but later told interviewer Terry Gross that he lapsed at the age of 12 after the death of a school friend and an uncle, followed by a feeling of receiving no useful answers from the church.

[16] In 1985, Oliver made his first on-screen appearance playing Felix Pardiggle, a minor role in the BBC drama Bleak House.

In an appearance on Late Night with Seth Meyers, he commented, "When I was six years old ... [the BBC] wanted a kid with dark hair and brown eyes, and I was two-for-two on that".

[20] Oliver's first major stand-up appearance was at the 2001 Edinburgh Festival Fringe as part of the late-night showcase The Comedy Zone, where he played an "oleaginous journalist".

[21] Oliver frequently worked with other members of the comedian group the Chocolate Milk Gang, including Daniel Kitson, Russell Howard, David O'Doherty, and Alun Cochrane.

[24] In 2003, Oliver manned the "results desk" on an election night episode of Armando Iannucci's satirical show Gash on Channel 4.

[9][27] Starting in June 2005, Oliver made appearances on British television as a panellist on the satirical news show Mock the Week, and became a frequent guest on the first two series.

[33] After moving to New York City, Oliver began performing stand-up comedy in clubs, later headlining shows in larger venues.

[67] Oliver has stated that he has full creative freedom, including free rein to criticise corporations, given HBO's ad-free subscription model.

[76] Oliver has guest-starred in several TV shows, including The Simpsons as Booth Wilkes-John (2014);[77] Gravity Falls as the voice of Sherlock Holmes (2012);[47] Rick and Morty as an amoeba named Dr Xenon Bloom (2013);[47] Randy Cunningham: 9th Grade Ninja as the voice of Coach Green (2012–15);[78][79] My Hero as a man from the BBC (2001);[80] Green Wing as a car salesman (2004);[81] Big Mouth as the camp counsellor Harry (2020);[82] and Bob's Burgers as a cat agent (2017).

[47] Oliver was originally cast in 2010 to star in the Terry Jones film Absolutely Anything as Neil Clarke,[83] but scheduling conflicts due to the debut of Last Week Tonight in 2014 led to the role being recast for Simon Pegg.

[84] In 2019, Oliver voiced the porcupine Steve in the CGI animated film Wonder Park and hornbill Zazu in the remake of Disney's The Lion King.

[89][90][91] Oliver has said that among his comedic influences are Armando Iannucci, David Letterman, Monty Python, Peter Cook, Richard Pryor,[25] and Jon Stewart.

[93] Edward Helmore wrote in The Guardian about Oliver's comedy, "His style leans toward the kind that Americans like best from the British – exaggerated, full of odd accents and mannerisms, in the vein of Monty Python.

[94] Oliver met Kate Norley, an Iraq War veteran who served as a medic in the U.S. Army's 1st Cavalry Division, at the 2008 Republican National Convention; he was reporting for The Daily Show and she was campaigning with Vets for Freedom.

[99] Oliver's immigration status when he joined The Daily Show in 2006 placed certain constraints on what he could do in the United States, but also provided him with comedy material as he poked fun at the opacity and occasional absurdity of the process of obtaining US residency.

[103] In an episode of The Bugle released on 2 November 2009 and recorded three days earlier, Oliver announced that he was approved for his US green card, noting that now he can "get arrested filming bits for The Daily Show".

[104] Oliver says he was given a scare while applying at the US embassy in London when an immigration officer asked, "Give me one good reason I should let you back in to insult my country" before following up with, "Oh, I'm just kidding, I love the show."

[107] Oliver was opposed to Brexit, writing multiple pieces about it and calling it "painful, it's pointless, and most of you didn't even agree to run it; you were just signed up by your dumbest friend".

[131][132][a] Members of Congress credited Oliver with helping to win a vote to enforce protections for chicken farmers who speak out about industry practices, after a Last Week Tonight segment on the subject.

[133][134][b] A Washington, D.C., council member proposed a resolution in Oliver's honour after he aired a segment on the district's struggle to attain statehood.

[140] One example of Oliver's investigative work is a segment on the Miss America organization, which bills itself as "the world's largest provider of scholarships for women".

[141] Oliver's team, which includes four researchers with journalism backgrounds,[142] collected and analysed the organization's state and federal tax returns to find that its scholarship programme only distributes a small fraction of the claimed "$45 million made available annually".

[153][154] In May 2018, actor Russell Crowe donated approximately $80,000 to the Australia Zoo wildlife hospital for the creation and naming of "The John Oliver Koala Chlamydia Ward".

[155] Oliver had previously bought in an auction several film props that had been used by Crowe, including his jockstrap from Cinderella Man, which he sent to one of the last Alaskan Blockbuster Video shops for exhibition.

[159] In August 2020, the mayor of Danbury, Connecticut, Mark Boughton, announced in a Facebook video his intention to rename the Danbury Water Pollution Control Plant as the "John Oliver Memorial Sewer Plant" as a comedic symbol of his displeasure at Oliver's hyperbolic insult to the city during a segment concerning alleged racial disparities in a jury selection process.

[161][162] As a response to Boughton's video, Oliver embraced the idea enthusiastically, promising to donate $55,000 to Danbury charities if the city renamed the sewage plant after him.

[162][163][164] After the city council voted 18–1 in favour of naming the plant after him, Oliver visited Danbury to attend the unveiling ceremony on 8 October 2020 in person, wearing a hazmat suit.