Born in Ålesund, Norway, to Jörgen Andreas Laurits Anderssen and Hanna Petrine Kristine (nee Johansdatter). He had five siblings. (Inga, b. 1881, Hanna, b. 1888, Gina Jensine, b. 31 August 1893, Gurine Thora, b. 12 February 1896, and Hans, b. 28 February 1893) The family lived on Kleven farm in Örskog and employed a servant. The household also had a foster daughter, Olivie O. Tendfjordnes, b.1898.

Olaus worked as a casual labourer and a sailore. In 1902 or 1903 he went to America with his brother Hans, where he lived in Hatton, North Dakota, working as a farm labourer. By 1908 he had a livestock farm in South Dakota and after a challenging period he made plans to visit his family in Norway. He travelled from New York to Glasgow in Autumn 1911.

By April 1912 he made his return to the USA. He registered his destination as Johan B. Abelseth 1112 Lincoln St. Minneapolis and travelled with five other Norweigians: Adolf Humblen, Anna Salkjelsvik, Peter Søholt (a cousin), Sigurd Hansen Moen (married to Olaus' sister Inge) and Karen Marie Abelseth.

Karen was only 16 but her family were neighbours of Olaus' family and her father asked him to look after her on the trip to America. The group sailed for Newcastle from Ålesund before making their way to Southampton to board the Titanic. Olaus shared cabin G-63 on F-Deck with Humblen. He was in his cabin near the bow of the ship when the disaster occured. He made his way along 'Scotland Road' to find Karen. He located her near the main third staircase towards the stern. The group then headed for the aft well deck.

They waited on the poop deck for instructions and at around 01.30 third class female passengers were ushered onto the Boat Deck, followe dby the men at 02.00. Olaus and his party made for the Boat Deck while many stayed on the poop deck. Karen was put into a lifeboat (possibly 16) by Olaus, Moen and Søholt.

As the last boats pulled away the call went up for sailors, some of the crew were working on releasing a collapsible boat and Olaus, with six years experience as a fisherman was tempted to help but his relatives encouraged him to stay with them.  Niether his brother in law or hsi cousin could swim and they found themselves near the fourth funnel as the ship started to sink beneath the icy water. They clung to a lifeboat davit and leapt into the water. Olaus got tangled in a line as he surfaced and once he had freed himself he could not see either of his relatives. 

Olaus was in the water for about twenty minutes before he made it to collapsible A. He pulled himself into the waterlogged boat after clinging to the sides. In the waist deep water of the lifeboat Olaus encountered a man from New Jersey who had shared his carriage on the boat train to Southampton. This man, suspected to be Arthur Keefe or August Schmidt and another man perished from the cold in the dawn light. Olaus is believed to have been responsible for keeping morale and spirits high with singing as the occupants sat in miserably cold conditions. 

On the Carpathia Olaus found coffee and brandy but without a cabin and slept o the deck in his sodden clothes.  

He spent a few days at St. Vincent Hospital in New York before testifying in the US senate inquiry and heading to Minneapolis. He briefly visited Canada before returning to his farm in South Dakota. He married Anna Grinde in July 1915. The couple had four children and they worked their farm for the next thirty years. 

He was often asked to recount his experiences by local schools and historical societies but eventually declined such invitations as reliving the tragedy became too uncomfortable for him. 

They retired and settled in North Dakota. Anna celebrated her 100th birthday in 1977 and passed away in August 1978. Olaus died on 4 December 1980.