Imam Mohammed Mahmoud told Sky News how he had just finished prayers when a “panicked” worshipper ran in to say what was happening outside.
“We arrived on the scene within minutes after the accident, we found the assailant on the floor being restrained by around three people,” he said.
“The injured and deceased brothers were being attended to and CPR was being administered on them.
“We found that a group of people quickly tried to collect around him and some tried to hit him, either kicks or punches.
“By God’s grace we managed to surround him and protect him from any harm. We stopped all forms of attack and abuse towards him that were coming from every angle.”
Imam Mohammed said he was with others trying to stave off violence against the perpetrator and he told police arriving on the scene that a “mob” was attempting to hurt him.
“If you don’t take him, God forbid, he might be seriously hurt,” he told officers.
Footage from the scene shows an angry crowd restraining the suspect after he drove a white van into pedestrians – many believed to be worshippers leaving evening prayers – at around midnight.
One person has died and eight have been taken to hospital following the terror attack. All of the casualties were Muslims, police say.
People were filmed screaming expletives and “killer” repeatedly at the van driver as he was held down in the chaotic situation.
Witnesses say Imam Mohammed urged people to leave the man alone, telling the crowd: “Do not touch him!”
He was also said to have used his body to shield the suspected terrorist from angry onlookers.
Adil Rana, 24, who was outside Finsbury Park Mosque when the attack happened, said the imam moved quickly to de-escalate the situation.
“The driver jumped out and then he was pinned down to the floor and people were punching him and beating him, which was reasonable because of what he’s done,” he said.
“And then the imam of the mosque actually came out and said: ‘Don’t hit him, hand him over to the police, pin him down’.”
Ibn Omar, a worshipper at the mosque, also saw the imam trying to stop people attacking the suspect.
“The assailant was on the floor, apprehended, some individuals were trying to injure him but obviously the general Muslims were saying that, ‘no don’t do that’,” he said.
“The imam as well was urging people that, ‘listen wait til the authorities come and apprehend him’.”
London mayor Sadiq Khan praised Imam Mohammed’s actions.
“When things were getting very heated, and we can understand why, Imam Mohammed did a really good job in calming things down and making sure that justice can be done as it should be done via due process, rather than anyone taking the law into their own hands,” he told Sky News.
“This is a good community. They pull together, they work closely with each other and the actions of Imam Mohammed are what I would expect from a good faith leader and a good Muslim leader.”
Toufik Kacimi, chief executive of the Muslim Welfare House, also praised the actions of Imam Mohammed, calling him a “hero”.
The leader’s “bravery and courage helped calm the immediate situation after the incident and prevented further injuries and potential loss of life,” he said.
Metropolitan Police Deputy Assistant Commissioner Neil Basu thanked members of the public who restrained the driver, saying “their restraint in the circumstances was commendable”.
The driver has been arrested on suspicion of attempted murder and terror offences.