Janene Jackson (right), Mayor Vincent C. Gray's director of policy and legislative affairs, is the latest high-profile departure from the mayor's office. Gray will leave office in January. (Executive Office of the Mayor, D.C./Courtesy of the Executive Office of the Mayor)

Janene D. Jackson, a top aide to D.C. Mayor Vincent C. Gray, is leaving early next month, further endangering Gray’s hopes of convincing the city council to approve a complicated land deal to build a a soccer stadium in his final months in office.

Jackson was among Gray’s first appointments after his victory in 2010. A former aide to D.C. Council Chairman Phil Mendelson, she was credited with restoring working ties between the offices of the mayor and council, which had grown hostile and dysfunctional during the tenure of Mayor Adrian M. Fenty.

She was also the city’s top liaison to Congress during tough years, as Gray often taunted congressional leaders over budget shutdowns and efforts to secure voting rights and statehood.

Jackson is the latest in a series of key departures from Gray’s inner circle since he lost the Democratic primary to Council member Muriel E. Bowser in April.

Pedro Ribeiro, Gray’s communications director, left this month for a senior post in the Department of Homeland Security. Gray’s directors of transportation and consumer and regulatory affairs have also left.

Janene Jackson (center), was Mayor Vincent C. Gray's director of policy and legislative affairs. Previously she held a top post at the D.C. Chamber of Commerce (Executive Office of the Mayor/Courtesy of the Executive Office of the Mayor)

Jackson will become senior counsel at Holland and Knight’s public policy and regulation group, practicing law and eventually lobbying, once a one-year prohibition for doing so with the District expires.

In an e-mail to senior staff members this week, Gray’s chief of staff, Chris Murphy, lauded Jackson for her service and patience in the seemingly “impossible task” of managing relationships between the mayor and council.

“I think we would all agree that Janene has had one of the toughest jobs — if not the actual toughest job — in the Administration,” Murphy wrote. “Janene managed to do it with extraordinary aplomb and with a fundamental spirit of respect and decency for both institutions ... aided by her trademark laugh and great sense of humor. We will miss her.”

According to Murphy’s e-mail, Jackson deputy James Pittman will become the mayor’s new director of the office of policy and legislative affairs.

Mendelson, the council chairman, said the loss of Jackson would force the council to “work harder to ensure the legislative and executive branches” communicate in coming months.

“She’s just very good,” he said. “Her leaving presents a challenge.”

Previously, Jackson was a senior vice president at the D.C. Chamber of Commerce.