In 1861 or 1862, he settles in Ecouen and becomes French citizen under the name of Dansart but continues to sign and write his name as Dansaert with an e. In 1863, he exhibits in Bruxelles and Paris, where he is invited there until 1889. His early paintings were of realistic style, showing historic sceneries, but they evolved toward a more intimacy one. He may have been influenced by his master, Pierre Edouard Frère and his friends.
On July 11th and 12th 1863, Noël Philippe Gaché, coal dealer, and Victorine Marguerite Cloux, sold for 1500F paid cash a house located 18 rue d’Ezanville (Ezanville street) to Marie Constant Dansaert, artist painter, and his wife Henriette Joséphine Agathe Louise Tassain. The house has a ground floor, two rooms and an attic above it, a small shed and a garden next to a little street.
Marie Constant Dansaert and Henriette Tassain had three children born in Ecouen. Godfathers were Philippe François Sauvage, painter artist living in Villiers-le-Bel and Arnoux Auguste Michel, painter artist living in Ecouen.
Léon Marie Constant Dansaert worked and lived for some times in Italy and in Germany. In 1864, he exhibited at the Salon of Anvers (Belgium), in 1867 at the Paris Universal exhibition and in 1881 at the Belgium art exhibition of Bruxelles (Belgium). From 1868 to 1889, his paintings are showing the 18th century typical family life and some Revolution time sceneries.
Following his wife’s death, on October 30 1876, he is left alone with five minor children to take care of. The house inventory shows a total value of 1750 F for all the artistic works inside, including: a marine view from Vernier for 50 F, a countryside from Léonide Bourges for 100 F, an other one from Desmarais for 100 F and four unfinished paintings from himself for 1500 F.
Some people lend him some money, like: on December 30th 1877, Marie Catherine Lacourte, from Presles (village near by Ecouen), for 2000 F and somebody else on May 12th 1891, for 5000 F.
Close to the end of his life, Marie Constant Dansaert donated one of his paintings to the Village of Ecouen: “Le serrurier dans son atelier” (the locksmith in his workshop).