Ian Johnson, a member of Ashursts' energy and major projects group, is currently negotiating departure terms from Ashursts, which may include a period of gardening leave.
Chadbournes hit the headlines in May when it advertised three £700,000 jobs for project finance lawyers, the highest salary ever publicly offered for a British lawyer.
Several partners from City law firms were reported to have applied for the jobs at the time, but Chadbourne has still not announced a decision on the appointments.
Johnson, who will be Chadbournes' first English partner, denies that he is getting a similar salary. He said: “Oil law is being increasingly globalised. Working for a US firm will not be very different because most of the clients are international.”
Chadbournes currently has three US partners in its London office and two associates, one of whom is English.