After launching Net-a-Porter in 2000 from her bedroom, former journalist Massenet leaves the company with a pay off believed to be in excess of £100m.
Yoox and Net-a-Porter agreed a merger in March to create a €1.3bn business which Massenet was set to chair.
Yoox said in a statement she will no longer be a member of the board of the new company:
Following Natalie Massenet's tendering of her resignation today as executive chairman of the Net-a-Porter Group, Ms Massenet will not be a member of the board of directors of the new group, which will result from the upcoming merger.
The firm also confirmed today that the merger has received all required antitrust clearances. As part of the deal Massenet was due to be handed a four per cent stake in the company worth £46m.