Two other top executives are also leaving and the finance chief is moving to an operational role, Clearwire said on Thursday.
Chairman John Stanton will replace Morrow on an interim basis at the head of Clearwire, which is seeking billions in funding to expand its high-speed wireless network and cutting costs in a push to deliver a profit in 2012.
Morrow, who has been CEO for two years, came to Stanton with personal reasons for resigning but the chairman, in an interview with Reuters, would not elaborate. They also discussed how Morrow's departure might be a good time to make other organizational changes Morrow had been considering, Stanton said.
Morrow did not elaborate when contacted by Reuters.
Sievert and Hart did not immediately respond to requests for comment.
The company said the changes will not hurt Clearwire's progress in resolving a dispute with 54 percent owner Sprint that has reduced Clearwire revenue in recent quarters.
Stanton said he expects an imminent agreement between the pair, which have been arguing about how much Clearwire charges Sprint for renting space on its network. He said it was a very complex issue that requires heavy lawyer involvement.
It's hard to put a fence around all these pieces and get them all done, he said.
Chief Commercial Officer Mike Sievert and Chief Information Officer Kevin Hart are also leaving to pursue other opportunities, according to Clearwire, which said their duties will go to existing employees.
The company said it promoted Chief Financial Officer Erik Prusch to the role of Chief Operating Officer and that company treasurer Hope Cochran will become CFO.
Stanton said Clearwire is still looking at all options for raising new funding, including the potential sale of wireless spectrum it does not need.
He declined to comment specifically on other relationships Sprint might be pursuing such as a merger with T-Mobile USA, a unit of Deutsche Telekom
But despite all this the executive said that Clearwire's relationship with Sprint is close.
We believe that will continue to improve and get strong, said Stanton, who was elected Clearwire chairman in January, replacing company founder Craig McCaw who resigned in late December.
Clearwire shares fell 2.6 percent in late trade to $5.60 after the news, losing some of its gains in the regular trading Nasdaq session where it had closed up 6.9 percent at $5.75.
(Reporting by Sinead Carew; editing by Ted Kerr, Phil Berlowitz)