O’Brien moved to Los Angeles upon graduating from Harvard to join the writing staff of HBO's Not Necessarily the News. He spent two years with that show, and performed regularly with improvisational groups like The Groundlings. He also acted in corporate infomercials to earn money during this period.
After Not Necessarily the News, O’Brien worked as the warm-up comic for The Wilton North Report, a Fox show that was on the air for just four weeks. O’Brien then moved on to the Happy Happy Good Show, a stage show being put on in Chicago, Illinois at the time.
In January 1988 Saturday Night Live's executive producer Lorne Michaels hired O’Brien as a writer. During his 3½ years on SNL he wrote such recurring sketches as "Mr. Short-Term Memory" and "The Girl Watchers", the latter of which was first performed by Tom Hanks and Jon Lovitz. O’Brien also wrote the sketch "Nude Beach", which became infamous due to the fact that the word penis appeared in it no less than 42 times, much of it in the form of song . He also appeared as an extra in some skits, occasionally with a speaking role. In 1989, he and the other SNL writers were awarded an Emmy Award for Outstanding Writing in a Comedy or Variety Series.
In the spring of 1991, O’Brien left SNL to write and produce a pilot for the television show Lookwell, starring Adam West. It was broadcast on NBC in July but was not picked up as a series. That Fall, O’Brien signed on as a writer and producer for the Fox series The Simpsons, where he also became a supervising producer. In a speech he gave at Harvard on Class Day in 2000, O’Brien credited The Simpsons with "saving" him, a reference to the career slump he was experiencing prior to his hiring for that show . Of the episodes he wrote while there, he considers "Marge vs. the Monorail" to be his favorite.
On April 26, 1993, Lorne Michaels chose O’Brien to be David Letterman's replacement as host of Late Night with David Letterman (with Andy Richter as his sidekick), and the show's name was changed to Late Night with Conan O’Brien. It received generally unfavorable critical reviews for the first 2-3 years after its debut. Indeed, the show was reportedly cancelled by network executives, but was allowed to remain on a day-to-day basis when it was realized there was no programming available to replace it.
Since then, however, O’Brien and the Late Night writing team have consistently been nominated for an Emmy Award for Best Writing in a Comedy or Variety Series, though they have not won as of 2005. In 1997, 2000, 2002, 2003, and 2004 he and the Late Night writing staff won the Writers Guild Award for Best Writing in a Comedy/Variety Series.
In the 2003-04 television season, Late Night with Conan O’Brien averaged 2.5 million viewers each week, easily beating out every other show in its time slot.
On November 9, 2005, O'Brien's wife gave birth to their second child, Beckett. 
O'Brien's comedy and mannerisms
- Clasps his hands and says 'yeah' during his monologue, between setup and punchline
- Often knocks over his desk microphone (on purpose)
- His sketches sometimes have a surreal tone
- Makes extensive use of chroma key, puppetry, and cheap-looking models pulled by threads
- Sometimes switches into a silly voice or affectation and back again, similarly to Robin Williams but not so manic; has joked several times that his real identity is the actor "Chip Whitley"
- Often jokes that his show is underfunded and unpopular due to its late time slot when it is, in fact, highly successful
- Often takes shots at NBC, saying how they are in the "ratings basement"
- Often moves outside the camera frame or very close to the camera during his monologue
- Often hops around like a bunny
- Often quiets applause of audience members prior to his monologue by saying "keep cool my babies" with hushing hand gesture.
- Often manipulates his pompadour
- Often makes fun of his red hair and large head
- Always does a hop and gestures toward the band at the beginning of his show
- Almost always comments on the audiences' applause before his monologue
- Often makes fun of Kirstie Alley and Ruben Studdard for being overweight. Paris Hilton, Michael Jackson, and Kevin Federline also make easy targets for him
- Performs the string dance at the request of guests on his show, and sometimes on his own
- Frequently displays his ability to move his hair up and down by using his forehead muscles
Conan Christopher O’Brien was born in Brookline, Massachusetts, a suburb of Boston. He is the third of six children in an Irish American family, one of four boys. His father, Dr. Thomas O’Brien, was a research physician at Brigham and Women's Hospital and an associate professor at Harvard Medical School, specializing in infectious disease. His mother, Ruth Reardon O’Brien, is a former partner of the Boston law firm of Ropes & Gray . His sister Jane is a comedy writer and producer.
After graduating as the valedictorian from Brookline High School (Brookline, Massachusetts), O’Brien entered Harvard University. Throughout his college career, he was a writer for the Harvard Lampoon humor magazine. During his junior and senior years, O’Brien served as the Lampoon's president, making him only the second person ever to serve as president twice, and the first person to have done it in 85 years. He graduated magna cum laude from Harvard in 1985 with a concentration in American History and Literature.
On January 12, 2002, O’Brien married (former) advertising copywriter Liza Powel in her hometown of Seattle, Washington, in a nuptial Mass at St. James Cathedral. They have one daughter, Neve, born on October 14, 2003 in New York City and a son, Beckett, born November 9, 2005 in New York City  .
O’Brien is a distant cousin of Denis Leary through marriage.
- "As for O’Brien, the young man is a living collage of annoying nervous habits. He giggles and titters, jiggles about and fiddles with his cuffs. He has dark, beady little eyes like a rabbit. He's one of the whitest white men ever." – Tom Shales, The Washington Post 
- "Somehow, Conan O’Brien has transformed himself into the brightest star in the Late Night firmament. His comedy is the gold standard and Conan himself is not only the quickest and most inventive wit of his generation, but quite possibly the greatest host ever." — Conan O’Brien, 2000 Harvard Commencement Speech .
- ^ Transcript from "Nude Beach" SNL sketch written by O'Brien
- ^ Text of O'Brien's 2000 commencement speech at Harvard from an ad-supported fan site
- ^ Conan To Replace Leno In 2009, a September 2004 CBS News article
- ^ ...O'Brien Not Worth a Hoot to the Night Owl, a 1993 review of O'Brien's show, from a fan's ad-supported, tripod.com-hosted website
- ^ Ruth Reardon O'Brien, from a Stanford University website
- ^ NBC Universal: Birth Notice from Late Night with Conan O'Brien
- Official website
- Interview with Conan on NPR's Fresh Air (September 8, 2003)
- 'Poonster Gets the Last Laugh and O'Brien Returns to Harvard, June 2000 articles from the Harvard Crimson
- Template:Imdb name
- Conan-O'Brien.net fansite