The gift from the Marcus Foundation, announced Friday, will expand the cash-strapped hospital's trauma center to six bays from four and create a 20-bed intensive care unit for victims of strokes and brain injuries.
Grady is the only Level One trauma center in Atlanta and is the major hospital for the poor and uninsured.
"I think everybody in the city of Atlanta and in the state of Georgia understands it's imperative for this hospital to succeed," said Mr. Marcus, who also founded the Georgia Aquarium. "We want to do our part."
The 950-bed hospital in downtown Atlanta is one of the nation's largest public hospitals and a mainstay for people who lack comprehensive medical insurance or who are on public health insurance programs.
Grady provides more than $250 million in charity care each year. It's had chronic financial problems, with net losses of about $37 million in 2008 and $35 million in 2007.
Mr. Marcus said his first gift to Grady was driven by a change in leadership at the hospital -- a new board and chief executive officer last year.
"I think Grady was poorly run," Mr. Marcus said. "This is a very significant vote of confidence on the future of Grady."
"It says worlds about where we've come at Grady," said Pete Correll, the chairman of Grady's board of directors. "Bernie is willing to have the Marcus name and quality image" at Grady. "It's going to save a lot of lives."