The Los Angeles native replaces her former boss, Steve Cooley, as the county's 42nd district attorney. She defeated Deputy District Attorney Alan Jackson in a contentious race in November.
"I often talk about my father and mother migrating here from the South to escape racism that was the backdrop of their lives," Lacey said as she reflected on the historic day. "I tell that story because it is a story of determination of faith and of true strength. It is that strength that I draw on."
The ceremony, which took place in the afternoon at the Galen Center downtown, was full of pomp and circumstances. But it was a far cry from Lacey's humble beginnings.
"The voters of this county allowed us to witness that it is possible for a girl from a working-class neighborhood like the Crenshaw District, who was educated in a public school like Dorsey High School, who worked her way up from the bottom, can become the district attorney of the largest prosecutorial offices in the nation," she said. "How cool is that?"
Lacey has 12 years of management in the District Attorney's Office under Cooley, who offered her advice at the ceremony.
"Be nonpartisan, stay away from politics as much as possible," he said. "Realize you are a constitutional officer with a very specific function."