Downs takes on this chief executive role after five years as executive director for science and enterprise at deafness charity RNID. He takes over from Ken Allen, who had been interim chief executive at the Society of Biology.
Downs said he wanted to continue the work of integrating the Biosciences Federation and the Institute of Biology, which merged to form the Society of Biology.
"A key challenge in the months ahead will be to ensure the society has a clear identity that brings together the expectations and then delivers results," he said. "There are exciting times ahead, for the society and for biosciences as a whole."