His mother, Charlotte Drouin de Vandeuil, married César-François Cassini in 1747 and they lived in the Paris Observatory where Jacques Cassini was effectively the director, although this official position was only created somewhat later. Dominique was born in the Observatory and was the eldest of his parents two children.
Kanyang ina, Charlotte Drouin de Vandeuil, may asawa Cesar-François Cassini sa 1747 at sila ay nanirahan sa Paris obserbatoryo kung saan Jacques Cassini ay epektibo ang direktor, kahit na ito ay opisyal na posisyon lamang nalikha tila mamaya. Dominique ay ipinanganak sa obserbatoryo at noon ay ang pinakamatanda ng kanyang mga magulang ng dalawang bata.