Lewis was born in Santurce, Puerto Rico and raised in Saint Thomas, U.S. Virgin Islands.

In 1995, she was nominated by President Clinton and confirmed by the Senate as Inspector General of the Department of the Interior.

In 1998, Lewis was nominated and confirmed as United States attorney for the District of Columbia, the first woman to serve in that position.

From October 2007 to December 2008, she served as managing associate general counsel at Freddie Mac.

In 2009, President Barack Obama nominated Lewis to be Assistant Secretary of the Interior for Land and Minerals Management.