Sgt. Gary Stein will get an other-than-honorable discharge and lose most of his benefits for violating the policies, the Corps said.
The San Diego-area Marine who has served nearly 10 years in the Corps said he was disappointed by the decision. He has argued that he was exercising his free-speech rights.
"I love the Marine Corps, I love my job. I wish it wouldn't have gone this way. I'm having a hard time seeing how 15 words on Facebook could have ruined my nine-year career," he told The Associated Press.
Gary Kreep, an attorney for Stein, said he would pursue administrative appeals within the Marine Corps but anticipates the effort will be denied. He said he planned to file an amended complaint in federal court.
"As long as he wants to pursue this, we will be supporting him," said Kreep, who is executive director of the United States Justice Foundation, an advocacy group.