The Greater Indianapolis Chamber of Commerce will lead economic development efforts for central Indiana as the result of a merger between four organizations approved Thursday.

The chamber will merge with Develop Indy, the economic development group for Marion County, as well as Indy Partnership and Business Ownership Initiative, the groups announced.

Indianapolis Mayor Greg Ballard and leaders of the four organizations approved the merger.

The merger has been in the works since Scott Miller, the former head of Develop Indy, became the chamber president in October. The proposed merger didn’t sit well with some members of the Indy Partnership, which represents surrounding counties.

But Miller said he thinks the merger will result in more money spent on marketing the city and region, as well as more economic development representatives out in the field, rather than doing administrative tasks. Indy Chamber’s revenue, about $5 million in 2011, will probably rise to $8 million to $10 million after the merger, he said Thursday. “We are actually hoping to grow those dollars.”

The chamber will grow from 30 employees to 50, he said.

The chamber has nearly 3,000 business members representing 235,000 employees in central Indiana, making it one of the largest regional chambers of commerce in the country.

Denver, Louisville, Nashville and Houston all have combined chambers of commerce and economic development organizations, according to Indy Chamber.

Each of the merged organizations will operate as a business unit of the chamber. Develop Indy is the largest of the three, with $2.9 million in revenue in 2010, according to the most recent tax information. Its not-for-profit board of directors was appointed by Ballard, and a large part of its funding has come from the Indianapolis Bond Bank.

“Aligning the strategic resources of these organizations with those of the chamber will better position our efforts to attract new jobs and grow existing companies,” Ballard said in a prepared statement. “The organizations’ shared goals of economic vitality and success for Indianapolis will only strengthen as we move forward in building a better future for our Hoosier work force.”

Indy Partnership has technically been part of Develop Indy, but it will become a separately operated and branded business unit, Miller said.

The Business Ownership Initiative, another division of Develop Indy that works with start-ups and provides micro loans, will also become a separate business unit.

All three of the merged organizations and the chamber have their offices in the Chase Tower in downtown Indianapolis. Miller said the transition team will be looking at future office space.