Micucci was born in Jersey City, New Jersey, to Italian parents. She grew up in Nazareth, Pennsylvania, in the Lehigh Valley region of the state, and was raised as a Catholic. She learned to play classical piano after being taught by her mother. Micucci graduated in 1998 from Nazareth Area High School. She then received an A.A. in Fine Arts from Keystone College in La Plume, Pennsylvania, and a B.A. in Studio Art in 2003 from Loyola Marymount University, Los Angeles.

Micucci’s TV credits include numerous television commercials, as well as acting roles, including Toni the barista on NBC’s Four Kings; guest roles on Malcolm in the Middle, ‘Til Death, How I Met Your Mother, Cory in the House, The Big Bang Theory, and Campus Ladies; and recurring roles on Scrubs and Raising Hope. Her film credits include The Last Hurrah, Bart Got a Room, and When in Rome. She played Lily the IT girl on Elevator, produced by HBO’s Runawaybox. In early 2009, she released a five-track EP entitled Songs.

Micucci appeared in five episodes of Scrubs (“My Lawyer’s in Love”, “My Absence”, “My Chief Concern”, “Our Histories”, and “My Finale”) as Stephanie Gooch, a ukulele player with whom Ted Buckland begins a relationship. She performs her song “Mr. Moon” and an adapted version of “Fuck You” (retitled “Screw You” for ABC), a song she typically performs as part of the musical duo Garfunkel and Oates. In 2009, she starred in the short film Imaginary Larry, co-written and co-directed by Riki Lindhome, her partner in Garfunkel and Oates. In August 2009, Micucci appeared in an advertising campaign for Hillshire Farms and for H & R Block in January 2010.

On December 30, 2009, G4TV named Micucci the #1 Woman of Comedy.

In 2010, Micucci appeared in the Kristen Bell film When in Rome and in an episode in the sixth season of the TV show Weeds as a slightly sedated waitress. She appeared in some episodes of the HBO series Bored to Death and appeared as the babysitter/dogsitter/eldersitter Shelley in the series Raising Hope. In February 2011, Micucci appeared briefly in a Progressive Insurance ad as a waitress. She has also voiced a character on Pendleton Ward’s animated series Adventure Time, and as the character of Julie Kane on the Disney XD animated series Motorcity. She also voices the recurring character Sadie on the Cartoon Network animated series Steven Universe. In July 2012, Kate appeared in Written by a Kid’s production Scary Smash, a Geek and Sundry creation that was executive produced by Kim Evey, Felicia Day, and Sheri Byrant.

In January 2013, Micucci’s casting was announced for a recurring role on The Big Bang Theory as “a potential love interest for … Raj.” Her character, the painfully shy Lucy, first appeared on February 14, 2013. Micucci appeared as a guest judge on King of the Nerds.

Since October 2015, Micucci has provided the voice of Velma Dinkley in various Scooby-Doo franchise projects, beginning with the animated television series Be Cool, Scooby-Doo!.

In 2016, she co-starred in a season one episode of the Netflix comedy-drama series Easy with Orlando Bloom and Malin Akerman, reprising her role for both the 2nd and 3rd seasons.

Micucci married musician and recording producer Jake Sinclair in February 2018. They live in Los Angeles and New York.