He is chief executive officer (CEO) of Inter-Con Security Systems, Inc., and a director of Wells Fargo & Company.

Under his leadership, Inter-Con has grown to be one of the largest security system providers worldwide, with 25,000 employees in North and South America, Europe, and Africa.

In 1993, Mayor Richard Riordan appointed Hernandez to the Los Angeles Police Commission, where he served as president through 1995.

He is also chairman of the board of regents of Loyola High School, vice chairman of the Los Angeles County Museum of Art, vice chairman of the Children's Hospital Los Angeles Board of Trustees, a director of the California Health Care Foundation, a trustee of the University of Notre Dame and of Pomona College, and a member of the National Infrastructure Advisory Council, Harvard College Visiting Committee, and the Harvard University Resources Committee.

Hernandez retired as non-executive chairman of McDonald's in May 2024, with president and CEO Chris Kempczinski assuming the role.