Concluding a week-long opening statement, prosecutor Brian Altman said Ashik Ali thought other members of the group would eventually calm down and "get married," The Daily Telegraph reported.
Ali admitted in police interviews following his arrest last year the plan called for him to wear a suicide vest and carry a gun, Altman told the court.
Ali, 27, Irfan Khalid, 27 and Irfan Naseer, 31, all from Birmingham, have denied a dozen charges they face include planning a bombing campaign, recruiting others for terrorism and terrorism fundraising.
Authorities say the men planned to detonate eight explosives-filled backpacks in public places.
Altman said Ali told police that Khalid and Naseer made martyrdom videos while allegedly at a terrorist training camp in Pakistan.
"He did not want to say what they had been planning," Altman said of Ali. "He said he had thought, 'Give it time and they will open a shop and get married.'"
The court heard last week Nasser borrowed about $160,000 to buy five AK-47 assault rifles and boasted he could buy a grenade for $2,400.
The trial continues.