A native of Wichita, Kansas, Buck studied character animation for two years at CalArts, where he also taught from 1988–1993. At CalArts, Buck became friends with both John Lasseter and Michael Giaimo, whom he would work with many years later on Frozen.:33
In 2008, Buck's old friend Lasseter (whom by then had become Disney Animation's chief creative officer) persuaded him to come back to Disney from Sony.:6,11 Around September 2008, Buck pitched three ideas to Lasseter, one of which was a fairytale musical version of the The Snow Queen; Lasseter liked the Snow Queen idea and authorized Buck to proceed with development.:6,11 After it was put on hold during 2010, the film was officially announced in December 2011 under the title Frozen, with a release date of November 27, 2013. In turn, Buck persuaded Giaimo to come back to Disney to serve as the film's art director,:33 for which Giaimo would go on to win the Annie Award for Best Production Design in an Animated Feature Production.
Buck is married to Shelley. They have three sons, Ryder, Woody, and Reed.
Their older son, Ryder, died at age 23 on October 27, 2013 in a car accident, when he was hit by two cars after his car broke down on the Glendale Freeway. Ryder was a singer and songwriter performing in his band Ryder Buck and the Breakers, and was recovering from a year-long battle with a Stage 4 testicular cancer. On March 2, 2014, upon accepting the Academy Award for Best Animated Feature for co-directing Frozen at the 86th Academy Awards, Buck dedicated the award to his son Ryder.
Reed lent his voice to Arnold, a little penguin from Surf's Up, directed by his father.