Sullivan & Cromwell has hired Adam Szubin, a former top official at the U.S. Department of the Treasury, where he was a key architect of the Obama administration’s controversial nuclear deal with Iran. Szubin will join the firm’s financial services group as of counsel in Washington, D.C.

“Sullivan & Cromwell’s unparalleled reputation, deep expertise, and international reach will enable me to add significant value for the firm’s clients in the U.S. and around the world,” Szubin said in a statement Monday. “I am thrilled to be joining their highly talented team.”