He said he has seen adoption change from a system mostly used by unmarried mothers to one used for children in care.
The 65-year-old, who adopted his two children through Camden Council, said: “It has been a wonderful combination of the personal and the professional.”
He added: “One of the things that has driven me is listening to children, and working directly with children, and recognising that it is fundamental to have a permanent, loving and stable family as we expect for all children.”
Dr Simmonds began his career as a social worker before becoming one of the first to teach a specialist course in child placement at Goldsmiths College in the 1980s.
He joined BAAF in 2000, and has become one of the most respected experts in adoption, fostering and looked-after children.
Caroline Selkirk, BAAF’s chief executive, said: “We are very proud of John and are thrilled that he and his work have been honoured.”