Incumbent agencies Norton PR and Crescendo PR will continue to work with Lego until the end of the year, with Engine-owned Mischief starting work in January, Lego said.
Mischief creative director Damon Statt said: "Lego Group has consolidated its PR briefs in the UK into one agency. We look forward to working with one of the most iconic and loved brands in the world."
Lego was voted the UK's most loved consumer brand in 2016 and 2017, placing above the likes of Adidas and Gucci, according to an annual brand passion report by social media analytics business NetBase.
It is unclear whether Lego's review of its UK media suppliers extends to marcoms disciplines beyond PR.
Meanwhile, PRWeek had learned that Lego PR and promotions manager Emma Owen left the business for a role at the Department for International Trade earlier this year. No replacement has been announced.
Lego 'stops funding hate'
In November last year, the toymaker said it would not run further promotions in the Daily Mail, following a campaign by the group Stop Funding Hate urging companies to pull their advertising revenue from newspapers that report negatively on foreigners.
A tweet from Lego in November said: "We have finished the agreement with The Daily Mail and are not planning any future promotional activity with the newspaper."
We have finished the agreement with The Daily Mail and are not planning any future promotional activity with the newspaper— LEGO (@LEGO_Group) November 12, 2016