Wilmington bought 30% of the gross revenue of Roxbury, which translates to a 60% ownership, said Charles W. King, vice president-media and investor relations.
Roxbury manages $4.5 billion, about half of which is for tax-exempt clients.
Three of the four owners of Roxbury -- Anthony H. Browne, Kevin P. Riley and Harry B. Wilson -- were given long-term employment contracts under the new structure. The fourth, James E. Moore, is retiring.
The structure also provides for other Roxbury employees to potentially receive options over time for 20% of the equity in the firm.
The deal could close in June.