The firms announced that they were in merger talks at the end of November, and the consultation and voting process concluded today, with approval from both partnerships.
The combined firm, to be known as Eversheds Sutherland, will come into effect on 1 February 2017, and will be led by join chief executives as part of a six-strong global management team.
Eversheds said there are "no significant internal structural changes anticipated within either firm and respective practice group heads will work together to co-lead client initiatives".
“Our strategic desire to have a platform in the US has long been public record," said Eversheds chief executive Bryan Hughes.
"The challenge has been finding the right firm, particularly one that shares the same vision as us and is a strong cultural fit. In Sutherland, we have found that firm. Eversheds Sutherland will give each firm’s clients a truly global platform, including strong US coverage.
"The feedback from colleagues and clients has been overwhelmingly positive, with many opportunities already identified, and we are very confident that this will be a great outcome for our clients and our people.”
Sutherland's managing partner, Mark Wasserman, said: "With this exciting combination, we will be able to offer clients of both firms the highest quality service and support around the world for their most important business opportunities.
"Both firms are focused on providing innovative, effective and efficient service in a changing global environment while maintaining cultures that value diversity, involvement in our communities and the importance of caring for our people. We look forward to building on the success of both firms as we work together for the future benefit of our clients and colleagues."
Earlier this month it was revealed that a record number of English solicitors have registered to work in Ireland since the Brexit vote.