Stephen I was only son of Odo, Count of Champagne, and Adelaide of Normandy, countess of Aumale, sister of William the Conqueror. Stephen succeeded his mother as Count before 1089.

In the conspiracy of 1095 against William Rufus, the object of the rebels was to place Stephen Rufus’s first cousin Stephen I Le Gros on the English throne. Stephen was the first cousin of brothers William Rufus, King of England and Robert Curthose, Duke of Normandy. The leaders were Robert de Mowbray and Guillaume III of Eu, Count of Eu. Stephen le Gros was apparently not put on trial himself as he may have been out of the king's reach in Normandy. Stephen's father Odo Count of Champagne lost his English lands for his complicity in the attempt to place his son on the throne of his first cousin William Rufus with a claim through his mother sister to William the Conqueror, Adelaide of Normandy Countess of Aumale.

In 1096 Stephen I, joined the First Crusade as part of the army of Robert Curthose who was his first cousin, Duke of Normandy. Following the death of King William Rufus, in 1102 Stephen I was given back his father's confiscated lands and became lord of Holderness, Yorkshire as his elder, England. He sided with Henry I his first cousin in 1104 against Robert II Curthose also his first cousin but in 1118, when William Clito who was the first son of Robert Duke of Normandy rebelled against his uncle Henry I of England, Stephen I supported him, with Baldwin VII of Flanders. He finally submitted to his first cousin Henry I in 1119.