Born to migrant farm worker parents, Lupe was raised in San Antonio as one of eight children. She started life working in the fields, but paid her way through college, earning a Bachelor's degree in Business Administration. She then earned a Master's degree in Criminology and Criminal Justice from the University of Texas at Arlington.
Prior to entering law enforcement, Lupe Valdez was an officer in the United States Army. During her time in the Army, she attained the rank of Captain. Her law enforcement career began as a jailer, first in a county jail and then a federal prison. She then moved on to investigative roles as an agent of the General Services Administration, the U.S. Department of Agriculture and, finally, the U.S. Customs Service where she was a leader in the federal Counter Smuggling Initiative.
With the creation of the Department of Homeland Security in 2002, she was made a Senior Agent, serving in that role until her retirement in 2004. In January 2004, Lupe retired to run for the office of Dallas County Sheriff.
On January 2, 2004, Lupe announced her candidacy for the Democratic nomination for Dallas County Sheriff. During the primary election, she faced three opponents, and finished as the highest vote-getter with 13,867 votes. She subsequently won a run-off election against future Dallas County Judge Jim Foster. Valdez won 73% of the vote in the run-off.
As she entered the general campaign, Valdez was widely considered the underdog in her general election race against Republican Danny Chandler. Chandler, a 30-year veteran of the Sheriff's Department, had defeated incumbent Sheriff Jim Bowles in the Republican primary. Bowles, who was tainted by corruption allegations, had held the office for 20 years.
The general election saw Valdez beat Chandler by 51.3% to 48.7% - a margin of some 18,000 votes. The election, combined with the fact that Valdez is female, Hispanic and a lesbian, made national headlines and was even reported overseas.
As an openly lesbian candidate for public office, Valdez's campaign won the backing of the Gay & Lesbian Victory Fund. She was sworn in on January 1, 2005. Valdez is a committed Christian, and formerly attended the pro-gay Cathedral of Hope of Greater Dallas.
Upon taking office as Dallas County Sheriff, Valdez faced a department that was wracked by poor morale, tainted by allegations of corruption and marred by the fact that the Dallas County Jail had begun failing state and federal inspections prior to her election. The jail had failed inspections because of poor sanitation conditions, a failing smoke evacuation system, unacceptable medical care, and a lack of sufficient guards to meet the legally-required guard-to-inmate ratio.
The Dallas County Jail has continued to fail inspections every year that Valdez has been in office.