San Francisco Supervisor Katy Tang won’t seek re-election in November, a decision that will end more than a decade of public service work at City Hall and create the first District Four election without an incumbent since 2006.

Tang said the “very difficult decision” to step aside from the board, where she represents the district she grew up in, came from a desire to find out what life can be like outside City Hall.

“At this point in my life, I felt like I’d really like a change in my career, a change of scenery,” said Tang, who is 34. “I always want to continue to serve people and give back in some way, but I want to stimulate myself and my intellectual growth in different ways.”

Tang has a reputation as a levelheaded and hard-working pragmatist who measures her success as a supervisor in terms of effective customer service.

As she considered the Tuesday afternoon deadline to file for the November ballot, “I had to think really hard about, after almost 12 years in this District Four office, do I want to serve another four years?” Tang said. She will see out the remainder of her term, which ends in January. District Four on the city’s west side includes the Sunset and Parkside neighborhoods.

Tang entered city government as an intern, working first for the Assessor-Recorder and later at the mayor’s communications office during the Gavin Newsom administration. In October 2006, she started a year-long stint as a staffer in the mayor’s budget and policy office, where she was pleased to be working behind-the-scenes.

“My aspiration at that time was to become a full-blown budget analyst — that was my dream,” she said.

But the fall of 2007, Newsom appointed Carmen Chu, a mentor of Tang’s in the budget office, to fill the District Four seat vacated by Ed Jew, who resigned as he was facing extortion and perjury charges.

Nani Coloretti, the city’s budget director at the time, asked Tang to become a legislative aide to Chu. The job was supposed to be temporary, but lasted 5½ years.

“I had never watched a board meeting in my life, never read a piece of legislation, so I had no idea what I was doing,” Tang said. “But what stuck with me the whole time was the notion of, well, when residents call us, it’s all about how we can solve their problems,” she said. “We always had with us ingrained the customer service aspect of our work.”

In February 2013, late Mayor Ed Lee appointed Chu to be the city’s assessor-recorder and picked Tang to fill her seat on the board. She was then elected to fill out Chu’s term and in 2014 was elected to a full term.

“She’s really about working in consensus and working with others, and I think that’s really a credit to her personality and style,” said District 11 Supervisor Ahsha Safaí, a close colleague of Tang’s on the board. “She’s completely dedicated to her constituents and her district, and I don’t think there’s anybody in this building that’s going to speak an ill word of her,” he said.

Tang highlighted her work in creating San Francisco’s local density bonus program, called HOME-SF, which offers incentives to developers to build low- and middle-income housing.

She’s also proud of her work to pass some of the strongest lactation-workplace policies in the country, requiring San Francisco businesses to provide employees breaks and private locations for lactating mothers. Tang’s ordinance inspired a similar state bill, SB 937, introduced by Sen. Scott Wiener, a former colleague on the Board of Supervisors.

Before her term ends, Tang said she hopes to pass legislation building on HOME-SF by providing more options for meeting affordable housing requirements. She’s also especially keen to see through a bill she introduced with Safaí last month that would streamline the permitting process for opening small businesses.

Tang said she plans to support Jessica Ho, one of her legislative aides, in her planned run for the District Four seat.

“When I first asked (Ho) if she had ever considered running for office, she said no. And it reminded me of myself,” Tang said.

“Being able to mentor a young, up-and-coming woman leader who had never otherwise considered running for public office brings me great joy, just like Carmen and Mayor Lee did for me,” she said.

Dominic Fracassa is a San Francisco Chronicle staff writer. Email: dfracassa@sfchronicle.com Twitter: @dominicfracassa