While performing shows with the Second City in 1997, Fey sent several scripts to NBC's "Saturday Night Live" ("SNL"). She had been asked to send them by "SNL"'s head writer Adam McKay. McKay was a former performer at Second City. She was hired as a writer for "SNL" following a meeting with "SNL" creator Lorne Michaels. Fey moved to New York. She told "The New Yorker", "I’d had my eye on the show forever, the way other kids have their eye on Derek Jeter." At first, Fey "struggled" at "SNL". Her first sketch to air starred Chris Farley in a Sally Jessy Raphael satire. Fey went on to write a series of parodies. This included one of ABC's morning talk show "The View". She co-wrote the "Sully and Denise" sketches with Rachel Dratch, who plays one of the teens.
Fey played an extra in one of the episodes in 1998. After watching herself, she decided to diet. By dieting she lost 30 pounds. She told "The New York Times", "I was a completely normal weight. But I was here in New York City, I had money and I couldn't buy any clothes. After I lost weight, there was interest in putting me on camera." In 1999, McKay quit as head writer. Michaels asked Fey to replace McKay. She became "SNL"<nowiki>'</nowiki>s first female head writer. Fey does not make a big deal about this accomplishment because there have not been very many head writers.
In 2000, Fey began performing in sketches. She and Jimmy Fallon became co-anchors of "SNL's Weekend Update" segment. Fey admitted she did not ask to audition, but that Michaels asked her to do it. Michaels explained that there was "chemistry" (connection) between Fey and Fallon. Michaels, however, said that choosing Fey was "kind of risky" at the time. Her role in "Weekend Update" was well received by critics. Ken Tucker of "Entertainment Weekly" wrote: "...Fey delivers such blow darts – poison filled jokes written in long, precisely parsed sentences unprecedented in "Update" history – with such a bright, sunny countenance makes her all the more devilishly delightful." Dennis Miller, a former cast member of "SNL" and anchor of "Weekend Update", was pleased with Fey as one of the anchors for the segment: "...Fey might be the best "Weekend Update" anchor who ever did it. She writes the funniest jokes". Robert Bianco of "USA Today", however, commented that he was "not enamored" with the pairing.
In 2001, Fey and the writing staff won a Writers Guild of America Award for "SNL"<nowiki>'</nowiki>s 25th anniversary special. The following year at the 2002 Emmy Awards ceremony, she and the writing team won the Emmy for Outstanding Writing for a Variety, Music or Comedy Program.
The pairing of Fey and Fallon ended in May 2004. Fallon left the show at the end of that season. He was replaced by Amy Poehler. It was the first time that two women co-anchored "Weekend Update". Fey revealed that she "hired" Poehler as her co-host for the segment. The reception to the teaming of Fey and Poehler was positive. Rachel Sklar of the "Chicago Tribune" noting that the pairing "has been a hilarious, pitch-perfect success as they play off each other with quick one-liners and deadpan delivery".
The 2005-2006 season was Fey's last. After it she left to make "30 Rock".
In 2002, Fey suggested a pilot episode for a situation comedy about a cable news network to NBC, who rejected it. The pilot was written again to focus on an "SNL" style series. It was accepted by NBC. She signed a contract with NBC in May 2003. It allowed her to remain in her "SNL" head writer position at least through the 2004–2005 television season. As part of the contract, Fey was to develop a primetime project to be produced by Broadway Video and NBC Universal. She began developing the pilot project under the working title "Untitled Tina Fey Project". The pilot, directed by Adam Bernstein, centered on the head writer of a variety show and how she managed her relationships with the show's star and its executive producer. In October 2006, the pilot aired on NBC as "30 Rock". Although the episode received generally good reviews, it finished third in its timeslot.
The network gave the series a second season, which began in October 2007. The show's third season premiered on October 30, 2008. The premiere episode set records for the highest ratings of the series. In January 2009, NBC renewed "30 Rock" for the 2009–2010 season.
In 2007, Fey received an Emmy Award nomination for Outstanding Actress in a Comedy Series. The show itself won the 2007 Emmy for Outstanding Comedy Series. In 2008, she won the Golden Globe, Screen Actors Guild, and Emmy awards all in the category for Best Actress in a Comedy Series. The following year, Fey again won the Golden Globe and Screen Actors Guild Award in the same categories. She was also nominated for an Emmy Award. In early 2010, Fey received a Golden Globe nomination for Best Actress. She won the Screen Actors Guild Award for Best Lead Actress.
In September and October 2008 Fey was a guest on "SNL" to perform a series of parodies of Republican vice-presidential candidate Sarah Palin. On the 34th season premiere episode, aired September 13, 2008, Fey imitated Palin in a sketch, alongside Amy Poehler as Hillary Clinton. Their act included Clinton making fun of Palin about her "Tina Fey glasses". The sketch quickly became NBC.com's most-watched viral video ever. It had 5.7 million views by the following Wednesday. Fey acted in the role again on the October 4 show. She also acted as Palin on the October 18 show where she was joined by the real Sarah Palin. The October 18 show had the best ratings of any "SNL" show since 1994. The following year Fey won an Emmy in the category of Outstanding Guest Actress in a Comedy Series for her acting as Palin.
In December 2009, "Entertainment Weekly" put her impersonation on its end-of-the-decade, "best-of" list, writing, "Fey's freakishly spot-on "SNL" impersonation of the wannabe VP (and her ability to strike a balance between comedy and cruelty) made for truly transcendent television."
In 2000, Fey worked with fellow "SNL" cast member Rachel Dratch in the Off Broadway two-woman show "Dratch & Fey" at the Upright Citizens Brigade Theater in New York City. The show was well received by critics. Tim Townsend of "The Wall Street Journal" in review of "Dratch & Fey", wrote that the fun part of watching them perform was "seeing how comfortable they are with each other". He said that the show "isn't about two women being funny. [...] Dratch and Fey are just funny. Period." One of the "SNL" sketches, "Sully and Denise", originated at Second City in Chicago.
On August 13, 2007, Fey was a guest on the children's television series "Sesame Street", in the episode, "The Bookaneers". She appeared as a guest judge on the November 25, 2007 episode of the Food Network program "Iron Chef America". Fey has appeared in Disney's campaign "Year of a Million Dreams" as Tinker Bell, along with Mikhail Baryshnikov as Peter Pan and Gisele Bündchen as Wendy Darling. She has also done commercials for American Express credit card.
On February 23, 2008, Fey hosted the first episode of "SNL" after the 2007–2008 Writers Guild of America strike. For this appearance, she was nominated for an Emmy in the category of Individual Performance in a Variety or Music Program.
In 2002, Fey appeared in the comedy "Martin & Orloff". She made her debut as writer and co-star of the 2004 teen comedy "Mean Girls". Characters and behaviors in the movie are based on Fey's high school life at Upper Darby High School. It is also based on the non-fiction book "Queen Bees and Wannabes" by Rosalind Wiseman. The cast includes other past cast members of "SNL" including Tim Meadows, Ana Gasteyer, and Amy Poehler. The movie received favorable reviews. It was a box office success, grossing $129 million worldwide.