Robert was born in 866 the posthumous son of Robert the Strong, count of Anjou, and the brother of Odo, who became king of the Western Franks in 888. West Francia evolved over time into France; under Odo, the capital was fixed on Paris, a large step in that direction. Robert and Odo's family is known as the Robertians.
Robert was present at the Siege of Paris in 885. He was appointed by Odo as the ruler of several counties, including the county of Paris, and abbot in commendam of many abbeys. Robert also secured the office of Dux Francorum, a military dignity of high importance. He did not claim the crown of West Francia when his brother died in 898; instead recognized the supremacy of the Carolingian king, Charles the Simple. Charles then confirmed Robert in his offices and possessions, after which he continued to defend northern Francia from the attacks of the Norsemen. Robert defeated a large band of Norse in the Loire Valley in 921, and the defeated invaders converted to Christianity and settled near Nantes.
The peace between the king and his powerful vassal was not seriously disturbed until about 921. The rule of Charles, and especially his partiality for a certain Hagano, had aroused some irritation; and, supported by many of the clergy and by some of the most powerful of the Frankish nobles, Robert took up arms, drove Charles into Lorraine, and was himself crowned king of the Franks (rex Francorum) at Rheims on 29 June 922. Robert's rule was contested by the Viking leader Rollo, who had settled in Normandy in 911 with the permission of Charles the Simple. During Robert's reign, Rollo remained loyal to Charles, who continued to contest his deposition. Collecting an army, Charles marched against the usurper and, on 15 June 923, in a battle near Soissons, Robert was killed, but his army won the battle, and Charles was captured. Charles remained a captive until his death in 929. Robert was succeeded as king by his son-in-law Rudolph, Count of Burgundy, also known as Raoul.