It is unclear whether the ruling means the suspension — also known as prorogation — will be reversed.
SNP MP Joanna Cherry QC, who was among the cross-party group of politicians who brought the action, tweeted: “All 3 judges in Scotland’s Highest court of appeal rule Prorogation unlawful!”
“Huge thanks to all our supporters & our fantastic legal team who have achieved the historic ruling that prorogation is unlawful,” she added in a second tweet.
More to follow.