Federal regulators signed off on Comcast Corp.'s bid to control NBC Universal, imposing an array of conditions aimed at preventing the cable giant from unfairly hindering competitors while making some of its first moves to regulate the emerging online video market.

The blessing by the Federal Communications Commission and the Justice Department seal a roughly year-long review and establish the ground rules under which Comcast must act as it tries to leverage NBC Universal's movie and television content to become a more high-profile...