Lacroix was born in 1991 in Paris, he was an only child, as his parents emigrated from Turkey and all of his siblings had died long before arriving in France. He attended ParisTech for a degree in biology and later a study aboard program in England, acquiring a doctorate in biology in 2017. He taught biology at Oxford University for several years before returning to France to work for CNES in Toulouse to train ESA astronauts for ISS crew rotation missions from the late 2010s until 2041. He was selected as the ESA's second slot on the Wanderer as the mission's exogeologist in 2042.