Roger was one of William the Conqueror's principal counsellors. He may not have fought in the initial invasion of England in 1066, instead staying behind to help govern Normandy. According to Wace’s Roman de Rou, however, he commanded the Norman right flank at Hastings, returning to Normandy with King William in 1067. Afterwards he was entrusted with land in two places critical for the defense of England, receiving the rape of Arundel at the end of 1067 (or in early 1068), and in November 1071 he was created Earl of Shrewsbury; a few historians believe that while he received the Shropshire territories in 1071 he was not created Earl until a few years later.
Roger was thus one of the half dozen greatest magnates in England during William the Conqueror's reign. William gave Earl Roger nearly all of what is now the county of West Sussex, which at the time of the Domesday Survey was the Rape of Arundel. The Rape of Arundel was eventually split into two rapes, one continuing with the name Rape of Arundel and the other became the Rape of Chichester. Besides the 83 manors in Sussex, his possessions also included seven-eighths of Shropshire which was associated with the earldom of Shrewsbury, he had estates in Surrey (4 manors), Hampshire (9 manors), Wiltshire (3 manors), Middlesex (8 manors), Gloucestershire (1 manor), Worcestershire (2 manors), Cambridgeshire (8 manors), Warwickshire (11 manors) and Staffordshire (30 manors). The income from Roger’s estates would amount to about £2000 per year, in 1086 the landed wealth for England was around £72,000, so it would have represented almost 3% of the nation’s GDP.
After William I's death in 1087, Roger joined with other rebels to overthrow the newly crowned King William II in the Rebellion of 1088. However, William was able to convince Roger to abandon the rebellion and side with him. This worked out favourably for Roger, as the rebels were beaten and lost their land holdings in England.
Roger first married Mabel de Bellême, who was heiress to a large territory on both sides of the border between Normandy and Maine. The medieval chronicler Orderic Vitalis paints a picture of Mabel of Bellême being a scheming and cruel woman. She was murdered by Hugh Bunel and his brothers, who in December 1077? rode into her castle of Bures-sur-Dive and cut off her head as she lay in bed. Their motive for the murder was that Mabel had deprived them of their paternal inheritance. Roger and Mabel had 10 children:
Robert de Bellême, Count of Alençcon in 1082, he succeeded his younger brother Hugh as 3rd Earl of Shrewsbury. He married Agnes, Countess of Ponthieu and died in 1131.
Hugh of Montgomery, 2nd Earl of Shrewsbury, died without issue 1098.
Roger the Poitevin,Vicomte d'Hiemois, married Adelmode de la Marche.
Philip of Montgomery.
Arnulf of Montgomery, married Lafracota daughter of Muirchertach Ua Briain.
Sibyl of Montgomory, she married Robert Fitzhamon, Lord of Creully.
Emma, abbess of Almenchêches.
Matilda (Maud) of Montgomery, she married Robert, Count of Mortain and died c. 1085.
Mabel of Montgomery, she married Hugh de Châteauneuf.
Roger of Montgomery, died young.
Roger then married Adelaide de Le Puiset, by whom he had one son, Everard, who entered the Church.
After his death, Roger's estates were divided. The eldest surviving son, Robert, received the bulk of the Norman estates (as well as his mother's estates); the next son, Hugh, received the bulk of the English estates and the Earldom of Shrewsbury. After Hugh's death the elder son Robert inherited the earldom.