The Sussexes first post, shared on Tuesday afternoon, quickly attracted attention.
Within 12 hours the newest account had collected more than 920,000 followers and followed just 21 pages, among them the three existing Royal accounts.
The post features the couple in several images, meeting with members of the public and engaging in projects.
Meanwhile, the description for Kensington Palace's account has been scrubbed to remove any mention of Harry and Meghan, and its profile picture has been updated to a family portrait of William, Kate and their three children.
The snaps show Prince Harry and the Duchess of Sussex photographed in countries around the world, including a previously unseen photo taken of the couple in Fiji during their royal tour a year ago and during visits to Morocco and Australia.
Meghan Markle and Prince Harry are the latest to be bitten by the social media bug, as the duo is now on Instagram.
"We thank you for your support, and welcome you to @sussexroyal".
The Duke and Duchess of Sussex are branching off from the rest of the Royal Family - at least on social media. They have been given permission by Queen Elizabeth II to base their household office at Buckingham Palace, while the couple themselves relocate to the idyllic estate of Windsor. The ROM also welcomed their newest followers (Meghan and Harry!) with a cheeky post of some their British royal collection. The implication is clear - they'll be using one of the most popular social media platforms in the world to spread their message.