His adoptive father died at the age of 40, when Willett was six, and he and his older sister, Donna, were reared by their mother, Doris, who waited tables to support the family.

After law school, Willett worked as a clerk for Judge Jerre Stockton Williams at the United States Court of Appeals for the Fifth Circuit.

[4] In April 1996, Willett joined then-Governor George W. Bush's administration as Director of Research and Special Projects, advising on various legal and policy issues.

In early 2002, Willett was appointed Deputy Assistant Attorney General for Office of Legal Policy at the United States Department of Justice, where he helped coordinate the selection and confirmation of federal judges.

Willett also led the development of an executive order to expedite U.S. citizenship for immigrant service members fighting in Iraq and Afghanistan.

For Constitution Day 2008, Willett authored a commentary in the Austin American-Statesman highlighting ConSource and its nonprofit educational mission to make these historical documents accessible to teachers, students, academics, lawyers and judges.

Willett was one of five incumbent justices on the 2006 ballot, but he was the only one who faced opposition; his four colleagues were unopposed in both the March 7 primary and the November 7 general elections.

The Review wrote that Smith seemed more intent in seeking "revenge for past losses than making a positive impact" on the high court.

Willett was liaison to the Texas Center for Legal Ethics and Professionalism, the Task Force to Ensure Judicial Readiness in Times of Emergency, and the Court Reporters Certification Board.

[1] On September 28, 2017, President Donald Trump announced his intent to nominate Willett to an undetermined seat on the United States Court of Appeals for the Fifth Circuit.

[10] On October 3, 2017, Willett was officially nominated to the seat vacated by Judge Emilio M. Garza, who assumed senior status on August 1, 2012.

SCOTUSblog described Willett as "more inclined to defer to the legislature in cases that he does not view as impinging on individual economic or religious liberty."

[21] In August 2018, Willett concurred dubitante when the court found that the Texas Medical Board was entitled to qualified immunity for an unconstitutional warrantless search it made of a doctor's patient records, writing: "To some observers, qualified immunity smacks of unqualified impunity, letting public officials duck consequences for bad behavior.

"[22][23] Willett was named Outstanding Young Alumnus of Baylor University in 2005 and inducted into the Forney High School Hall of Honor in 2007.