Norway, Denmark and Canada all approved the membership of the two new Nordic members on Tuesday, the same day the accession protocol was signed.
Estonia and Iceland ratified the accession protocol on Wednesday.
"Estonia is among the first to seal the deal and did so with lightning speed. I count on a speedy process from all Allies," the Estonian Prime Minister Kaja Kallas commented in a tweet.
There are now 25 remaining member state legislatures that need to approve Finland and Sweden joining the alliance and there are some lingering concerns that it will not be as smooth as the first five ratifications.
Even though the Turkish government approved Finland and Sweden to be invited to Nato, the decision still needs to pass through the country's parliament, as there is some uncertainty over the trilateral agreement signed by Turkey, Finland and Sweden at the Madrid summit last week.
