Marguerite Mongenast-Servais (1885–1925), was a Luxembourg women's rights activist.
She was married to the engineer Paul Mongenast. She was engaged in several progressive associations, among them the anti-monarchist "Action républicaine".
She was also a member of the women's rights organization "Organisation pour les Intérêts de la femme". There was never any organized women suffrage movement in Luxembourg: women suffrage was introduced in 1919 without any debate, as a part of the project of the new democratic constitution, and the women's rights organizations mainly focused on educational opportunities. However, in 1917–1919, Marguerite Thomas-Clement belonged to the few who spoke in favour of women suffrage in public debates through articles in the press.