Muhammad Oda Dakhlalla, 23, of Starkville, pleaded guilty before U.S. District Chief Judge Sharion Aycock of the Northern District of Mississippi, the Justice Department said in a statement.
Dakhlalla was remanded to the custody of the U.S. Marshals Service for sentencing at a later date, the statement said. His attorney declined comment.
Dakhlalla and his fiancée, Jaelyn Delshaun Young, 20, were arrested last August at Golden Triangle Regional Airport in Columbus, Mississippi, according to a criminal complaint. They were accused of conspiring and attempting to provide material support and resources to the terror organization ISIS.
"Our story will be that we are newlyweds on our honeymoon," the young woman allegedly wrote.
But the couple actually had planned to fly from Mississippi to Europe and then travel to Syria to join ISIS, the complaint said.
Young is to face trial in June, according to the U.S. Attorney's Office. CNN reached out to her attorneys but did not get an immediate response.
'We learn very fast and would love to help'
Court documents detailed what federal investigators said were the couple's plans, as allegedly communicated through social media to the undercover FBI employees over the past several months.
Among the allegations:
-- Young wrote of her plans to marry Dakhlalla so the two could travel to Syria together. She allegedly confirmed that the wedding took place in June, and said the couple's cover story would be that they were flying to Europe on their honeymoon. To avoid suspicion, "We won't be flying to Istanbul. We will fly to a different country and take a bus."
-- The couple described their skills and asked how they could help the terror group's efforts. "I am good with computers, education and media," Dakhlalla allegedly wrote in one message to an FBI employee. "What could I contribute?" Young also allegedly told an undercover FBI agent that her skills would be useful. "I am skilled in math and chemistry and worked at an analytical lab here on my college campus. My partner is very good with things like computer science/media. We learn very fast and would love to help with giving medical aid."
-- In messages detailed in the complaint, the couple seemed enthusiastic, but also concerned about how training would work once they arrived. "Salaam again," Dakhlalla allegedly wrote in a message to an FBI employee. "I wanted to ask about the military experience there. Would I be with people that speak English as well or do they put me with everyone at basic training? I am excited about coming ... but I feel I won't know what all I will be doing."
Son of imam, daughter of police officer
According to a law enforcement official, Dakhlalla is the son of a local imam, Young is the daughter of a Vicksburg, Mississippi, police officer and a recent convert to Islam.
Both are former Mississippi State University students, according to university spokesperson Sid Salter. Dakhlalla graduated with a degree in psychology, and Young was last enrolled in last year as a sophomore studying chemistry.