Upon earning her law degree, Joan was hired as a prosecutor and advanced from misdemeanor court to Chief Felony Prosecutor, Special Crimes Gang Prosecutor, and Legal Counsel to the Organized Crime Narcotics Task Force. She served as lead prosecutor in over 100 jury trials, including murders, aggravated robberies, and sexual assaults of adults, and children. Senator Huffman earned a reputation as a fair and tough enforcer of the law both as a prosecutor and a twice elected Judge to the 183rd Criminal District Court in Harris County.

Senator Huffman was first elected to the Texas Senate in 2008 and has been re-elected four times. She currently serves as Chair of the Senate Special Committee on Redistricting, Chair of the Senate Committee on Jurisprudence, Vice-Chair of the Senate Committee on Criminal Justice, as a senior member of the Senate Committee on Finance, the Senate Committee on Administration, and the Legislative Budget Board.

Senator Huffman's common sense approach to solving issues has allowed for her to build strong relationships with members of both parties, which enables her to represent the needs of her district and her constituents efficiently and effectively. Her leadership has been acknowledged by numerous advocacy groups. She was named as the "2017 Hero for Texas Children" by the National Center for Missing and Exploited Children, and a "Big Voice for Little Texans" by Court Appointed Special Advocates for her work to protect children. She is also the only three-time recipient of the Texas District and County Attorneys Association's "Law and Order Award" since its inception, for her efforts to improve victims' protections and the criminal justice system.