SE1's two hospitals gained NHS foundation trust status on Thursday, following an announcement by the independent regulator.
Guy's and St Thomas' chief executive Dr Jonathan Michael was one of 40 people to abseil from the top of the 469ft Guy's Tower on Sunday to raise money for the Evelina Children's Hospital.
Celebrating the news, chief executive Dr Jonathan Michael said: "I am delighted that we have been licensed to become one of the first wave of NHS Foundation Trusts. Being a Foundation Trust will give us greater flexibility to deliver improved services to our patients and to strengthen our engagement with local communities, our staff and the thousands of patients we treat each year."
In preparation to become a Foundation Trust, a members' council made up of patients, local people, staff and the Trust's partner organisations has been established. The members' council comprises 10 public, 10 patient and 7 staff members, all elected from the membership, together with 10 representatives nominated from local organisations.
Dr Michael added: "The Members' Council will provide support and advice to the Trust so we deliver services that best meet the needs of patients and the communities we serve.
"We already have over 13,500 members of our Foundation Trust, but I would like to encourage even more people to join as members, in particular individuals from the diverse ethnic communities that we serve in Lambeth and Southwark."
The first formal meeting of the Members' Council took place on Thursday at Guy's Hospital.