Born in Lathuy Castle, Jodoigne in the Austrian Netherlands (now Walloon Brabant, Belgium) in 1725, Beaulieu joined the Habsburg army in 1743 and fought in the War of the Austrian Succession. During the Seven Years' War he served first as an infantry officer and later on the staff of Feldmarschall Leopold Joseph von Daun. Beaulieu was wounded in the Battle of Kolin and also fought at the battles of Leuthen, Hochkirch, Maxen, and other actions. He received the Knight's Cross of the Military Order of Maria Theresa in 1760. "As a young man, his bold and fiery character combined with his great energy and constant activity had made him well-suited to the military life."