Mohamed Soltan, who had been a dual U.S. and Egyptian citizen, had been jailed since 2013 and in April was sentenced to life in prison for his support of the Muslim Brotherhood.
"He's home! So happy to see you, habibi. God is good," Kareem El-Hosseiny, one of Soltan's close friends, said in a Facebook post, using an Arabic term of endearment.
Soltan's family claimed he didn't belong to the Muslim Brotherhood, which Morsy once led and which is now banned in Egypt, according to the state-run Ahram Online website.
El-Hosseiny posted a picture on Facebook of Soltan 27, looking frail in a wheelchair after his arrival in Washington on Saturday.
Prior to his release, Soltan had been on a hunger strike for at least 14 months
-- during which the U.S. State Department called for his release on humanitarian grounds.
On Saturday, a senior official from the same department welcomed Soltan's release.
"We believe this step brings a conclusion to this case, and we are glad Mr. Soltan will now be reunited with his family in the United States," said the senior State Department official said.
His health is "dire," his family said in a statement. "He will receive medical treatment as soon as he arrives on U.S soil and will spend the immediate future with his family recovering."
Detained two years
Attorneys for his family said in a statement that Soltan had been "wrongfully detained for nearly two years and sentenced to life in prison for simply participating in peaceful protests and facilitating media coverage" for organizations such as Al Jazeera, ABC, The New York Times and Time.
"(Soltan) was tried alongside 50 other political prisoners in a Kafkaesque political show trial," the lawyers said. "He protested the deplorable conditions of his incarceration and his abuse in custody with the first and longest hunger strike in the Egyptian prison system."
Soltan renounced his Egyptian citizenship as part of the terms of his release, Ahram Online reported, citing one of his lawyers.
He'd resisted doing so, but his "family and lawyers pressured him to give up his nationality as there was no other option," said attorney Halem Henish.
Regardless of what it took, Soltan's release was cause for celebration back in America.
"Mohamed Soltan is free!" tweeted Suhaib Webb, the influential imam of the Islamic Society of Boston Cultural Center. "Allah is the greatest!"