The past year has been a whirlwind for Rhiannon Giddens, the Grammy-winning musician who became the first woman and first nonwhite person to win a major prize for excellence on the banjo and then celebrated the release of her latest album, “Freedom Highway,” with a performance at the Sing Sing Correctional Facility.

But none of it prepared her for what initially seemed like an innocuous call last month from an unfamiliar number in Chicago.

“I had fantasized about that moment ever since I knew it existed,” Ms. Giddens, 40, said, recalling the day she learned she was among the 24 people chosen as 2017 fellows of the John D. and Catherine T. MacArthur Foundation. “I was sitting in a cafe somewhere on tour, and I was just super-shocked and overcome.”

The fellowship, which honors “exceptionally creative people,” comes with a no-strings-attached grant of $625,000, to be awarded over five years. It is known colloquially as the “genius” award, to the sometime annoyance of the foundation.