Sir Keir Starmer has said suspected arson attacks on a house he owns and another property linked to him are "an attack on democracy".
The prime minister was speaking publicly about the blazes for the first time.
A 21-year-old man remains in custody on suspicion of arson with intent to endanger life, following three fires over the past week.
Emergency services were called to fires at the doors of two homes in north London within 24 hours of each other. One blaze was around 1.35am on Monday at a house in Kentish Town, while another was at a house converted into flats in nearby Islington the previous day.
There was also a third fire where a car connected to the politician was set alight on the same street as the Kentish Town property last Thursday.
Nobody was hurt in any of the suspected arson attacks, though the Kentish house's entrance was damaged.
Counter-terrorism police are investigating whether the three fires are linked, and say they are all being treated as suspicious.
Speaking at Prime Minister's Questions on Wednesday, Sir Keir said: "This is an attack on all of us, on democracy, and the values we stand for."
He was responding to comments made by Conservative leader Kemi Badenoch who said she wanted to express "how horrified" she was to hear about the incidents.
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Ms Badenoch added: "It is completely unacceptable, and I think I speak for the whole House when I say that this wasn't just on him, but on all of us, and our democracy."
Sir Keir said her comments were "absolutely right".
The prime minister also added that Ms Badenoch "did actually message me pretty well straight away" and said he really appreciated her support.
Liberal Democrat leader Sir Ed Davey said: "Can I offer my support to the prime minister and his family after the appalling arson attacks on his home, and can I echo his thanks to our brilliant police and firefighters."
What do we know about the fires?
Neighbours of the Kentish Town home described hearing a loud bang and said police officers were looking for a projectile.
It is understood Sir Keir still owns the property, but it is now being rented out after the prime minister and his family moved into 10 Downing Street, following Labour's general election victory last July.
On Tuesday, Dominic Murphy, the head of the Metropolitan Police's counter-terrorism command, said the force is "working at pace and continue[s] to explore various lines of enquiry".
"The protection of MPs is something we take extremely seriously across the whole of policing."
Commander Murphy added that any MP who is concerned should get in touch with the force.
He also said there will be an increased police presence in the area over the coming days.