Walcott needed a waiver from Commissioner David Steiner because he is not a licensed school superintendent.
Steiner said in his decision Thursday that Walcott has had a long and distinguished career and that his knowledge of educational issues is unquestioned.
Walcott is Bloomberg's deputy mayor for education. He has taught kindergarten, headed the Urban League and started a mentoring program for young boys.
Black quit after a rocky three months. She also received a waiver from the state to serve as chancellor although she had no background as an educator.