The management change had been in the works since Hovsepian elevated to the dual posts of president and chief operating officer was last November.
The Novell board said Messman and Tibbetts would leave Novell's employment "effective immediately" although Messman will remain on Novell's board through October.
"We will maintain a sharp focus on meeting customer demand and delivering value through Linux-based, enterprise-wide solutions and identity and resource management products," said Hovsepian in a statement.
Hovsepian joined Novell in June 2003 after working at various venture capital and investment banking firms. Before that, he held a number of executive positions at IBM over a 17-year period.
Novell's stock jumped initially more than 7 percent on the news. The firm's stock had dropped more than 30 percent in preceding months, however.
Novell said Dana C. Russell, the firm's current vice president of finance and corporate controller, will serve as interim CFO.
The Novell board praised the two departing executives, citing Messman's role in moving the company to adopt an open-source software strategy.