The news was announced by the couple’s publicist who said the pair will “maintain a close friendship and remain united in their love for their children”.
“They kindly ask for privacy,” the statement continued. “There will be no further comment.”
The couple first met on the set of the BBC drama Nostromo in 1996 and married in Tuscany one year later.
The pair have two sons together and Firth has another child from a previous marriage.
Firth and Giuggioli previously split in 2015 after the Italian businesswoman admitted to having an affair with journalist Marco Brancaccia.
The relationship was exposed when Giuggioli accused Brancaccia of stalking her.
“A few years ago Colin and Livia privately made the decision to separate,” the couple’s publicist said in a statement in March 2018.
“During that time Livia briefly became involved with former friend Mr Brancaccia. The Firths have since reunited.”
The statement continued, “Subsequently, Mr Brancaccia carried out a frightening campaign of harassment over several months, much of which is documented. For obvious reasons, the Firths have never had any desire to make this matter public.” The case was later dropped and settled out of court.
Firth previously discussed his relationship with Giuggiol during an interview on Piers Morgan‘s US talk show in 2011.
“You just navigate things on a daily basis,” Firth told the presenter.
“We are crazy about each other. We’re very committed on a daily basis to how we deal with our family lives.
“But the real secret is time – we have to make sure that we spend enough time together. Every relationship in life you’re going to have to take care of, there’s a marathon factor to it.”