Lappin, who ran unsuccessfully for Manhattan borough president last year, will take charge of the Downtown Alliance's business improvement district, which provides sanitation, marketing and other services for Lower Manhattan.
Lappin replaces Elizabeth Berger, the former Downtown Alliance president and longtime advocate of Lower Manhattan, who died of pancreatic cancer in August.
“I am thrilled to be joining the Downtown Alliance and eager to lead such an accomplished team," Lappin said in a statement. "It is particularly exciting to be taking the helm at the Alliance at this point in the district’s history."
In the City Council, Lappin represented the 5th District, covering the East Side of Manhattan, from 2006 to 2013. She chaired the Council’s Land Use Subcommittee on Landmarks, Public Sitting and Maritime Uses. She added three new parks to Manhattan and opened waterfront areas to the public.
Lappin ran in a four-way race for Manhattan borough president last year, but she came in second to Gale Brewer.
Cherrie Nanninga, the chief operating officer of real estate giant CBRE's tri-state region, led the search committee to find Berger's replacement and said she was impressed by Lappin's credentials.
"We feel really thrilled that we were able to attract a person as qualified and with a profile like Jessica's," Nanninga said. "She will be able to move forward and carry Liz's legacy."
Lappin, who graduated from Stuyvesant High School and then attended Georgetown University, said she is eager to get to work at the Downtown Alliance.
"The transformation unfolding in Lower Manhattan is inspiring,” Lappin said in the statement. “Few places anywhere can boast of the constellation of game-changing projects underway and nearing fruition. Lower Manhattan is an extraordinary place. Working on behalf of the area’s businesses, residents, workers and visitors will be an honor and a privilege. "