Early in his career, Greenberg held an Orthodox pulpit on Roosevelt Island in New York City. Since 1985, he has been a Senior Teaching Fellow and Director of the Diversity Project at CLAL – the National Jewish Center for Learning and Leadership, an interdenominational Jewish think tank, leadership training institute, and resource center. He is a co-founder and director of Eshel, a support, education and advocacy organization for orthodox LGBT Jews that saves lives and families. He is also on the faculty of the Shalom Hartman Institute of North America, a project of the Shalom Hartman Institute.