Massenet will co-chair with José Neves, chief executive, founder and executive co-chairman of Farfetch.
The Farfetch Group includes Farfetch.com, Browns, Black & White, and Store of the Future.
Massenet's focus will be growing the group's global brand and strengthening its partnerships with the fashion industry.
"I have, since Net-A-Porter launched, been a huge admirer of Natalie, she really is the undisputed pioneer, paving the way for the rest of us by demonstrating that not only could luxury be sold online but also that the internet would eventually become the primary way consumers engage with brands, globally," Neves said.
On her part, Massenet said that she appreciates what Farfetch has done to "rewrite the rulebook on how technology can work alongside bricks and mortar to elevate the customer experience".
Massenet added: "José is a true innovator, and I am thrilled to join him as he grows Farfetch into the online platform of choice for luxury fashion".
Since its launch in 2008, Farfetch has grown into one the top full-price destination for luxury shopping in terms of traffic, according to Alexa, Comscore and SimilarWeb.
Massenet founded Net-A-Porter.com in 2000, and expanded the company to include TheOutnet.com, MrPorter.com, Porter magazine, and social shopping platform, the Netset.