The combined data from the House of Commons Library showed that the SNP has around 125,500 members, over a thousand more than the Conservative Party.
Data is taken from media reports, party head offices, and press releases, as well as data from the Electoral Commission that was released last week.
Membership of the SNP rose by around 7,000 in the second quarter of 2018, something the party attributes to a surge in support after MPs walked out of the Commons chamber in protest at a so-called ‘Brexit Power grab’.
Electoral Commission figures showed that the Conservatives now make more money in bequests from deceased supporters than membership fees, prompting claims of a ‘membership crisis’ in the party.
The Commons membership figures estimate that Labour has around 540,000 members, with the SNP the second largest party on 125,500, the Conservatives on 124,000, while the Lib Dems have around 99,0000 members.
SNP Business Convener, Derek Mackay MSP said: “Over 7,000 people joined the SNP in just five days in June, propelling us ahead of a waning Tory party which is at risk of imploding completely over Brexit.
“As today’s figures reveal, the SNP continues to go from strength to strength. We continue to build the case for Scotland’s future, built on hope and optimism. And now more and more people agree that independence is the only way to deliver a fairer and more prosperous Scotland.
“With independence polling at historic highs, and SNP membership surging, we are more determined than ever to secure the best future for Scotland