Police confirmed the "extremely dangerous" McCann had been arrested in Cheshire after a two-week search and a stand-off with officers overnight.
The 34-year-old is now being investigated over seven incidents across Cheshire, Manchester, Lancashire, London and Hertfordshire between April 21 and Sunday.
The attacks involved a total of 12 victims, aged between 11 and 71, the Metropolitan Police said.
Describing the incidents as "grotesque and appalling", Commander Simon Rose said the force is relieved he has now been detained, adding that "England is a safer place".
He said it is "impossible" to know whether there are further victims, but the force has appealed for anyone else affected by McCann's actions to come forward.
He urged people who have been in contact with the suspect between February, when he was released from prison, and May to come forward.
Speaking outside Scotland Yard Mr Rose said: "I think we're exceptionally relieved that he's in custody and exceptionally grateful for the help and support we've had of so many members of the public in all the calls.
"These were and they are a grotesque and appalling series of offences that are thankfully exceptionally rare so it's extremely important that he is in custody and that England is a safer place."
Residents described how police descended en masse on a rural lane near Congleton in Cheshire on Sunday night after McCann fled up a tree.
Two 14-year-old girls were forced into a car in the Cheshire town earlier on Sunday.
The black Fiat Punto made off from the town centre at around 6.45pm, but was spotted and pursued by officers before it hit another car and the driver fled, leaving the victims unhurt but "extremely shaken", Cheshire Police said.
The suspect was found in the tree in Smithy Lane, a country road just outside the town, following road checks and closures.
Negotiators and paramedics were deployed and he was eventually taken into custody at around 3am on Monday morning.
Scotland Yard detectives had launched a hunt for suspected rapist and kidnapper McCann after he snatched two women in their 20s off the streets in north London on April 25 in separate incidents.
McCann is also suspected of abducting a 21-year-old woman at knifepoint in Watford four days earlier in the early hours of April 21 and raping her.
On Sunday, another series of attacks took place.
Police said a woman aged in her 30s was falsely imprisoned at a location in Haslingden, Lancashire, on Sunday morning at around 8am and, during the same incident a teenage girl and boy, aged 11, were raped.
At 1.30pm on the same day, a woman aged 71 was abducted and raped in Bury, Manchester.
Two hours later two 13-year-old boys and a 13-year-old girl were abducted in Heywood, Manchester.
During that incident the 13-year-old girl was sexually assaulted, police said.
The Metropolitan Police is leading the investigation and said McCann, who is in custody, is being brought to London.
Officers believe McCann was being hidden by a friend or family member, but Mr Rose said he could not go into any further details on that matter at this stage.
He said police have an "open mind" as to whether anyone else was involved in the incidents.
Asked if police regret how long it took to capture McCann, Mr Rose said: "We will be debriefing what happened. We will be always committed to identifying opportunities for learning."
The Ministry of Justice launched an urgent review after it emerged McCann may have been wrongly released from prison.
He was freed automatically halfway through a three-year sentence for burglary and theft - but should have gone before a parole board, it is understood.
McCann was subject to a life-long licence after he was released from prison in 2017 having served 10 years of an indeterminate sentence for public protection for a previous aggravated burglary.
Scotland Yard offered a reward of up to £20,000 for information leading to his arrest and prosecution.