De Ruyter was born on 24 March 1607 in Vlissingen, in the Dutch Republic, as the son of beer porter Adriaen Michielszoon and Aagje Jansdochter. Little is known about De Ruyter's early life, but he probably became a sailor at the age of 11. It is said that when he was a child he climbed up ladders to get to the roof of his home town's church. Not knowing De Ruyter was there, some workers then removed the ladders. De Ruyter had to lift tiles on the church roof to get into the church and out the door.
In 1622, during the Eighty Years' War against Spain, he fought as a musketeer in the Dutch army under Maurice of Nassau against the Spaniards during the relief of Bergen-op-Zoom. That same year he rejoined the Dutch merchant fleet and steadily worked his way up. According to English sources, he was active in Dublin between 1623 and 1631 as an agent for the Vlissingen-based merchant house of the Lampsins brothers. Little is known about his whereabouts in those years, yet it is known De Ruyter spoke the Irish language fluently.
He occasionally travelled as supercargo to the Mediterranean or the Barbary Coast. In those years, he usually referred to himself as "Machgyel Adriensoon", his name in the Zealandic dialect he spoke, not having yet adopted the name "De Ruyter". "De Ruyter" most likely was a nickname given to him. An explanation might be found in the meaning of the older Dutch verb ruyten or ruiten, which means "to raid", something De Ruyter was known to do as a privateer with the Lampsins ship Den Graeuwen Heynst.
On 16 March in 1631, he married a farmer's daughter named Maayke Velders. On 31 December that year, Maayke died after giving birth to a daughter; who also died just three weeks later. In 1633 and 1635, De Ruyter sailed as a navigating officer aboard the ship Groene Leeuw ("Green Lion") on whaling expeditions to Jan Mayen. At this point he did not yet have a command of his own. In the summer of 1636 he remarried, this time to a daughter of a wealthy burgher named Neeltje Engels, who gave him four children – one of whom died shortly after birth. The others were named Adriaen (1637), Neeltje (1639) and Aelken (1642).
In the midst of this, in 1637, De Ruyter became captain of a private ship meant to hunt for the Dunkirkers, raiders operating from Dunkirk who were preying on Dutch merchant shipping. He fulfilled this task until 1640. After sailing for a while as skipper of a merchant vessel named De Vlissinge, he was contacted again by the Zeeland Admiralty to become a captain, this time of the Haze, a merchant ship turned man-of-war carrying 26 guns, in a fleet under admiral Gijsels fighting the Spanish, teaming up with the Portugues during their rebellion.
A Dutch fleet, with De Ruyter as third in command, beat back a Spanish–Dunkirker fleet in an action on 4 November 1641, off Cape St. Vincent. After returning, he bought his own ship, the Salamander, and between 1642 and 1652, he mainly traded and travelled to Morocco and the West Indies to amass wealth as a merchant. During this time, his esteem grew among other Dutch captains as he regularly freed Christian slaves by redeeming them at his own expense.
In 1650, De Ruyter's wife, who in 1649 had given him a second son named Engel, unexpectedly died. On 8 January 1652, he made the widow Anna van Gelder his third wife and decided the time had come to retire. He bought a house in Flushing, but his blissful family life did not last long.