Ordinary people were having their lives disrupted by environmental protests, which Mr Sunak called “completely unacceptable”.
“This afternoon I sat down with all the police chiefs to make it clear that they have my full support in acting decisively to clamp down on illegal protests," said Mr Sunak, who joined the start of the conference hosted in Downing Street on Thursday.
“It is completely unacceptable that ordinary members of the public are having their lives disrupted by a selfish minority.
“My view is that those who break the law should feel the full force of it, and that’s what I am determined to deliver.”
Chief Constable BJ Harrington, the National Police Chiefs’ Council lead for public order and safety, said the meeting showed a “joint commitment to tackling criminal activism while respecting lawful protest”.
“We are not anti-protest but we are anti-crime," Mr Harrington said.
"Police are committed to responding quickly and effectively to activists who deliberately disrupt people’s lives through dangerous, reckless and criminal acts.
Mr Harrington, the head of Essex Police, said forces were “fully prepared to deal with further disruption planned ahead of Christmas”.
Earlier Metropolitan Police Commissioner Sir Mark Rowley said efforts by officers were having an effect and he was “absolutely determined” that anything going beyond lawful, reasonable protest would be dealt with.
But he also admitted that some trials might not take place for two years amid delays in the criminal justice system.
“We are currently giving the police new powers so that they can clamp down on these illegal protests," Mr Sunak said.
“They will have my full support in acting decisively and rapidly to end the misery and the disruption that’s being caused to ordinary families up and down the country.
“I’ve said to the police that whatever they need from government they will have, in terms of new powers.”
Met Police assistant commissioner Matt Twist said after the meeting: “The actions of activists Just Stop Oil continue to take up valuable officer time that could be better used in local communities and dealing with priority crime.
"That meant yesterday we had 180 officers taken away from their day-to-day duties.
“Indeed, since they started their campaign on October 2, there have been 46 days of action, which have taken over 12,500 dedicated officer shifts … equating to more than £5.5 million [$6.7 million].
“Everyone has the right to protest but some of their activity is not protest, it has been simple criminality, intent on disrupting London.
"We have arrested 755 people to date, and have so far charged 182 for a range of offences, from obstruction of the highway to conspiracy to intentionally or recklessly cause public nuisance."
Earlier, Sir Mark told the London Assembly: “Frankly, what I’ve seen is that Just Stop Oil have got much less assertive in their recent protests, frankly as a consequence of a large number of their leaders being remanded in custody as a result of our operations.
“I’m absolutely determined that anything that goes beyond lawful reasonable protest by creating serious disruption to London, by creating damage to property, will be dealt with robustly.
“That’s why we’ve used the more serious offences such as the statutory offence of public nuisance. We put the best part of 60 offenders before the courts at one stage for that offence.”
This week, Just Stop Oil protester Jan Goodey, who caused “mile after mile” of tailbacks on the M25 after climbing up a gantry, was jailed for six months after pleading guilty to causing a public nuisance.
Goodey, 57, was part of a demonstration on behalf of the climate group which forced authorities to close sections of the UK’s busiest motorway during the morning rush-hour on November 7.
In September, Goodey, from Brighton, East Sussex, was handed a two-year conditional discharge for obstructing the highway in a separate protest last year.
District Judge Daniel Benjamin said he had “flagrantly ignored” previous warnings that his conduct “was not acceptable in a peaceful and democratic society”.