A tool 10 is provided for radially expanding a downhole tubular C, and includes a central tool mandrel 12 which functionally is part of a drill string or work string, a tubular expander 48 at the lower end of the tubular, and a downhole actuator 15 for forcibly moving the expander axially within the downhole tubular. Slips 20 are positioned for securing the tool within the tubular, so that the slips may be set, and the tool subsequently stroked to move the expander 48 and radially expand a length of the tubular. Upward pull on the work string may expand long portions of the downhole tubular.