After college, Santo-Tomás worked as a stockbroker and financial analyst in Washington, D.C., but returned to Raleigh to pursue her interior design hobby as a career. She launched Working Girls, an interior design business and workroom, and then moved to Atlanta, where she continued her business and later became a partner at Third Millennium Development Inc. Santo-Tomás' career in television began with "Trading Spaces," and she is also a designer on "Trading Spaces: Family."