The Labour peer, who is stepping down as chair of the Social Enterprise Coalition, will take charge of the advisory group's first meeting on 3 September.
Membership of the group is yet be finalised, but Sarah Wood, director of the National Programme for Third Sector Commissioning at the Improvement and Development Agency, said she hoped to appoint a team of 18 - six from government departments and 12 from the voluntary sector.
The first of the 2,000 public sector trainees, who will be asked to champion the voluntary sector within their organisations, are expected to begin courses in January. Third Sector minister Phil Hope has indicated his willingness to join them.
The Government's third sector review, which was published last month, said that funding for the scheme, which is being introduced to increase understanding of the voluntary sector, would continue until 2011.
Wood said: "Two thousand isn't that many when you think it covers government departments, local government and primary care trusts, among others."