Dylan Makepeace, 24, was arrested after a group of boys "bravely" followed him on their bikes and detained him until police arrived.
The shocking spate of attacks took place over the space of just half an hour, on November 27 last year.
Each of Makepeace's victims bravely found him off, using house keys and a mobile phone.
Makepeace, of Mile End Road, began his spree around 5.30pm.
Two women noticed him following them to their flat block in Cleveland Way, Bethnal Green. He then followed them up to their floor, despite earlier having asked them how to get to a different floor.
Alarmed, one of the women began filming him, when he launched a sudden, physical attack on them both.
Both women fought back and hit out at Makepeace.
A "significant" struggle followed, in which Makepeace pushed the women to the floor and pinned them to the ground.
He ran away after one of the women hit him with a mobile phone. The women were left with cuts and scratches, and called the police to report the attack.
Around 6pm, Makepeace approached a third woman as she walked home from the gym, and followed her into the communal entrance of her apartment block on Cambridge Heath Road.
Once inside, the woman tried to stand to one side in the hope he would pass her.
But he instead grabbed her and put his hand over her mouth.
"She tried to scream and he told her to 'shut up'," said a Met Police spokesperson in a statement.
"She had her house key in her hand and she tried to hit him with the key. In the struggle they both fell over, he put his fingers down her throat as she tried to scream. He also hit her head hard onto the ground.
"Makepeace then began calling her offensive names before sexually assaulting her by touching her over her clothing.
"The woman continued to fight back and managed to hit him with her keys. Makepeace ran off when some boys on bikes appeared outside the apartment block."
Another resident heard the woman’s screams, took her into their flat and called police.
When officers arrived, they were flagged down by a group of young men on bikes who had followed Makepeace and detained him.
Makepeace was arrested, and later linked to the first incident through a police line-up.
Makepeace pleaded guilty at Snaresbrook Crown Court to two counts of assault by beating, one count of sexual assault on a woman, intentional strangulation, and one count of Section 20 GBH.
On Thursday, he was sentenced to five years imprisonment, with an additional three years on license.
He has been placed on the Sex Offenders Register for life, and was also issued with a Sexual Harm Prevention Order.
Detective Sergeant Michael Dixon, who led the investigation for the Met’s Central East Safeguarding team, said: “Dylan Makepeace is very clearly a danger to the public and especially lone women.
"He was opportunistic and violent in his approach. He specifically targeted women as they returned home and entered private residential areas to carry out his attacks.
“I want to pay tribute to the bravery of these three women. They all showed incredible fortitude as they supported our investigation. I am in no doubt that London is a safer place with Dylan Makepeace behind bars.”