Discover on Tuesday hired a former general counsel of the U.S. Department of Commerce as interim legal chief—a move that follows Capital One acknowledging that its hope of wrapping up its $35 billion purchase of the credit card giant by year-end is no longer realistic.

Kelly Welsh—a 35-year legal veteran who also was general counsel of Northern Trust Corp. and Ameritech, a Baby Bell created by the 1984 breakup of AT&T—succeeds Hope Mehlman, who in late August agreed to become chief legal officer of Ally Financial.