Olaf came from the Nordic - Gaelic Uí Ímair Dynasty. His father Guthfrith, the king of Dublin and Jorviks was expelled 927 of the Anglo-Saxon King Æthelstan of York.
Then Olaf organized a powerful coalition against Æthelstan. He landed in the same year with a large fleet in the North East of England, united with his father, the Scots King Constantine II and the British of Strathclyde under King Owain I. The alliance overran York and moved further south and conquered Limerick. Olaf and Constantine tried to rid himself of Æthelstans rule. He led the troops against non-English King Æthelstan of England at the Battle of Brunanburh, but was allied with the Danes ( from Dublin), Scottish and Welsh by King Æthelstan defeated. Olaf Guthfrithsson survived and fled with a few men over the sea back to Dublin.
After 939 Æthelstans death he returned to Northumbria back, conquered York and moved further south, besieged in vain Northampton and plundered the area of Tamworth. At Leicester he met King Edmund I., but there were no other significant battle, as the archbishops Odo of Canterbury and Wulfstan of York could mediate a peace treaty. Edmund I. had to recognize him as ruler over all areas north of Mercia.
941 Olaf plundered the church of St. Baiter and burned Tiningham down. Soon after, he was killed, whereupon the Northumbrian Lindisfarne devastated.