Finneas Baird O'Connell (born July 30, 1997), also known mononymously by his first name (sometimes stylized in all caps), is an American singer-songwriter, record producer, and actor. The recipient of numerous accolades, he has written and produced music for various artists, most notably for his younger sister, Billie Eilish, and is credited on all of her projects.

For his work with Billie Eilish, he has won 10 Grammy Awards among 21 total nominations, including nominations for the Big Four categories. He made history as the youngest act to win the Producer of the Year, Non-Classical category. He has won Record of the Year twice in a row, Album of the Year, Song of the Year, Best Pop Vocal Album, and Best Engineered Album, Non-Classical as a producer on Eilish's albums and songs. He was also nominated for Best New Artist for his solo work. Their song "No Time to Die" from the film of the same name earned him an Academy Award, a Golden Globe and another Grammy. Two years later, for their song "What Was I Made For?", they won the Grammy Award for Song of the Year, along with the Academy Award for Best Original Song and the Golden Globe for Best Original Song. They became the youngest two-time Academy Awards winners ever.

In addition to frequently working with Billie Eilish, he has also worked with other high-profile artists, including Drake, Kid Cudi, Nicki Minaj, Selena Gomez, Camila Cabello, Demi Lovato, Halsey, Justin Bieber, Karol G, Girl in Red, Rosalía, Tove Lo, Ringo Starr, and Tate McRae, and contributed to several film scores. O'Connell has released several singles as a solo artist, and his debut EP, Blood Harmony, was released in October 2019. The EP includes "Let's Fall in Love for the Night", his most successful song to date, peaking at number 17 on the US Billboard Alternative Songs chart. His debut studio album Optimist was released through Interscope Records in October 2021. He released his second album, For Cryin' Out Loud!, in 2024.

Finneas starred in the 2013 independent film Life Inside Out. He is also known for his role as Alistair in the Fox musical comedy-drama series Glee. He has also made an appearance on the American sitcom Modern Family.