The European head of legal at Marathon Oil & Gas, John Southworth, is leaving his position to head the upstream oil and gas practice at Nabarro Nathanson.
Nabarros sees the recruitment of Southworth - an energy specialist - as a "springboard" to expand its energy practice.
Marathon has decided not to fill the position of European head of legal. Instead, it will promote Sandra Majerfleisch to legal manager for UK production, another of Southworth's titles.
Southworth's appointment at Nabarros follows the departure from the practice earlier this year of upstream energy partner Mark Saunders, who joined New York firm Dewey Ballantine.
A Nabarros spokesman says the firm has continued practising upstream energy work with partner Gareth Jones crossing over both areas.
Nabarros' energy and infrastructure practice is headed by downstream expert Robert Tudway. Tudway will continue to focus on electricity and distribution, remaining the overall head of the energy group, including the upstream practice, which focuses on the exploration, extraction and development of oil and gas.
Southworth says: "After having spent a considerable amount of time working on the in-house side of the oil and gas industry I felt that it was the right time to move over to private practice."
David Bramson, Nabarros senior partner, says: "The firm's energy practice is growing. Earlier in the year we recruited projects and infrastructure partner Mary Bonar from Wilde Sapte and now we look forward to John Southworth's contribution to the practice."