Stella McCartney was slammed for the "disrespectful" post, which has since been deleted from Instagram.
Social media users labelled the post "insensitive", "inappropriate" and "tacky".
"Remembrance Day is to honour those that fought for us not to use for advertising purposes. Pretty shocked," said one follower.
Another said: "Using Remembrance Day to advertise your clothes is a little disrespectful! People died and you take pictures of people showing respect for advertising purposes. Just wrong."
While another wrote: "Not an appropriate time to be selling your clothes. This is extremely tacky. I expect better of you, Stella."
Meghan has attended a number of Remembrance events over the past week.
The Duchess and her husband, Prince Harry were part of a Remembrance ceremony at Westminster Abbey on Thursday, ahead of Remembrance Day - also known as Armistice Day - on November 11.
The Duke and Duchess of Sussex stood for a two-minute silence to remember those who have died in service of their country.
The couple then led the proceedings and planted wooden crosses in the Field of Remembrance.
The Duke, wearing his military uniform, saluted and paid his respects to the fallen, before walking back in the small crowd.
Meghan then followed, also planting her cross and lowering her head as sign of respect.
This was the first time Meghan had joined Harry at the Field of Remembrance.