Barry O'Callaghan, through his ownership of Riverdeep led the 2006 purchase of Houghton Mifflin and a year later the acquisition of Harcourt from Reed Elsevier, has resigned as CEO of Houghton Mifflin Harcourt. He is being replaced on an interim basis by CFO Michael Muldowney. A HMH spokesperson said the board will conduct an international search for a new CEO and will consider internal and external candidates.

The integration of Houghton Mifflin and Harcourt was a rocky one and in 2009 the publisher refinanced the company’s debt in part by converting HMH’s lenders' debt to equity and in the process diluting O’Callaghan’s stake in the publisher. Another refinancing was completed approximately one year ago. O’Callaghan, who had been chairman of HMH parent company Educational Media & Publishing Group, took over as CEO of HMH from Tony Lucki in April 2009.

O’Callaghan will remain a senior advisor to HMH.