Smith began her career at the Sheriff's Office in 1973, working as a Matron at the Santa Clara County Jail until 1976. She then became one of the first female permanent undercover vice cops. In three years in this position, she posed as a prostitute, a vendor of stolen goods, and a drug user. She next worked in the patrol division, then became a watch commander over the jails.
Assistant Sheriff, 1990-1998
In 1990, Sheriff Chuck Gillingham promoted her to Assistant Sheriff. In 1992, a male deputy filed an internal complaint against Smith after being transferred out of the narcotics unit while a female deputy with less seniority was allowed to remain. Smith stated that it was not her decision. The same deputy later filed a sexual harassment complaint against Smith, but she was found innocent.
Sheriff, 1998-Present
After eight years as Assistant, Smith was elected Sheriff of Santa Clara County on November 3, 1998 by a substantial margin and took office on December 15, 1998, becoming the first female sheriff in California.
1998-2010
After Santa Clara County District Attorney Dolores Carr made a controversial decision not to prosecute on grounds of insufficient evidence in an alleged rape of a 17-year-old in San Jose in March 2007, Sheriff Smith declared the case "still open" and that she believed a sexual assault did occur. Carr submitted the case to the Office of the State Attorney General for review.
Fourth term, 2010-2014
In 2010, Metro Silicon Valley credited Smith with putting the sheriff's office on a sound and efficient basis. She was re-elected in 2010. A lawsuit in 2011 claimed that Smith issues concealed carry permits preferentially to friends and donors. In 2012, there was controversy over Smith's assigning a bodyguard to Santa Clara County Supervisor George Shirakawa, Jr., who was ultimately convicted of misuse of funds and other crimes. The bodyguard was a family friend of Shirakawa's whose brother was a political advisor, and was reassigned by the Sheriff's Office after criticism.
Fifth term, 2014-2018
In June 2014 Smith won election for a fifth term against retired Sheriff's Captain Kevin Jensen, who had been endorsed by the Santa Clara County Deputy Sheriffs' Association and the Santa Clara County Correctional Peace Officers' Association. On August 27, 2015, mentally-ill inmate Michael Tyree was beaten to death by three jail guards who were convicted of second-degree murder in 2017. Two inmates escaped from custody in San Jose in November 2016. Two inmates escaped from custody in Palo Alto in November 2017. On June 5, 2018, Smith ran for re-election to her sixth term against five challengers including former undersheriff John Hirokawa and Deputy Joseph LaJeunesse. The results required the first run-off of her career, against Hirokawa, on November 6, 2018; Smith was re-elected. In 2019 The Mercury News and affiliates have uncovered that she issues CCW permits in a "pay for play" fashion to those who donate money to her campaign reelection funds. as well as shoddy record keeping. The Santa Clara County DA has opened an investigation into this issue