Murren, who has been chairman and CEO since 2008, has a contract to serve until the end of 2021, according to company filings with the SEC. Under the employment agreement, Murren is paid a base salary of $2 million a year with the opportunity for performance bonuses of 200% of his base salary as well as restricted stock grants .
The company said Murren will continue to serve as chairman and CEO until a replacement CEO is named.
A board committee “is working with a nationally recognized executive search firm to promptly identify and evaluate candidates to assume the role of Chief Executive Officer,” the company said in a statement.
"We have a solid leadership team in place, and I am confident that they will work with my successor to continue the Company's trajectory of growth and expansion," Murren said, according to the statement.
Shares of MGM fell in after-hours trading, losing $1.62, or 4.8% $32.04. Shares rose 2.9% in the regular session.
In the broader markets, the S&P 500 index rose 21.70 points, or 0.65%, to close at a record 3,379.45.
The Nasdaq Composite Index rose 87.02 points, or 0.9%, to end at 9,725.96, also a record.
Most of the major S&P 500 sub sectors rose.
The energy sector rose 5.56, or 1.36%, to 415.03.
The consumer staples sector traded flat at 659.83.
Among major market indicators, U.S. 10-Year treasury yields rose 5 basis points to 1.63%.
West Texas intermediate oil rose $1.63, or 3.26%, to $51.57 a barrel.
Gold fell $1.15, or 0.07%, to $1,566.80 an ounce.