Losinga was born in Exmes, near Argentan, Normandy, the son of Robert de Losinga (who later became Abbot of New Minster, Winchester).
Losinga was educated in Normandy, and took his vows at Fécamp Abbey in Normandy, of which he eventually became prior. While serving in this office he was invited to England by the king, William Rufus, who appointed him abbot of Ramsey Abbey.
Losinga was consecrated Bishop of Thetford in 1090 or 1091. He received the appointment having paid the king a sum of £1,900 pounds, as part of a deal in which Herbert's father was also made Abbot of Winchester. In 1094 he went to Rome to ask for forgiveness from Pope Urban for this act of simony. On his return he transferred the see from Thetford to Norwich, in accordance with the decree of Lanfranc's synod of 1075, that bishops should have their sees in the principal town of the diocese.
In addition to Norwich Cathedral, Losinga was responsible for founding St Margaret's Church, King's Lynn, the Church of St Nicholas in Great Yarmouth, and Norwich School.
Losinga visited Rome for a second time in 1116, representing the king in a dispute between the monarch and Anselm, the Archbishop of Canterbury. It may have been on the return journey that he fell severely ill at Placentia (modern Piacenza); other sources suggest he suffered this illness on a possible third journey to Rome, which he did not complete, instead awaiting his fellow ambassadors at Placentia, before returning to England with them.
One of Losinga's last public appearances was at the funeral of Queen Matilda on May Day 1118. He died on 22 July 1119 and was buried before the high altar of Norwich Cathedral.
Fourteen sermons and 57 letters written by Losinga have survived.