Chris Cotterill, chief of staff to Indianapolis Mayor Greg Ballard, plans to leave the administration and return to private business, the city announced Wednesday.

City-County Councilman Ryan Vaughn has resigned from his seat to replace Cotterill, the city said.

Cotterill, a former attorney for Barnes & Thornburg LLP, took over as chief of staff after the resignation of Paul Okeson in December 2009. He previously served as corporation counsel for the city and as general counsel for the state’s office of technology.

Vaughn has served as a City-County Councillor, including a two-year stint as president, representing the 3rd District since 2007. He resigned his council seat effective Wednesday and will leave his job as an attorney at Barnes & Thornburg.

According to state law, the Marion County Republican Party chairman must call a caucus of precinct committee members in the district within 30 days to elect a replacement for Vaughn.

“I am proud to have Ryan join our administration,” Ballard said in a prepared statement. “Ryan has served as president of the City-County Council, as a deputy prosecutor and as an attorney, and our city is very fortunate to have him continue his public service in this new capacity.”

Cotterill overhauled the city’s equal-opportunity program, spearheaded the adoption of Ballard’s ethics-reform plan and increased prosecutions against civil code violators, the city said. He also led negotiations in a $1.92 billion deal to transfer the water and wastewater systems to Citizens Energy Group.