Southwood received his PhD from Imperial College, London, in 1966 and was appointed as lecturer in the physics department in 1971, where he rose to become head of department in 1984. He studied the propagation of waves in the solar and terrestrial environment, joined the Galileo spacecraft team, and was also involved with the solar probe, Ulysses, and Cassini, the Saturn orbiter.

In 1997, Southwood left Imperial on a three-year leave of absence to become head of the Earth observation strategy at ESA, a post he held for over two years. He is currently Imperial College pro-rector. "It will be hard to succeed Roger Bonnet", says Southwood. "However, it is wonderful to have been given the opportunity."