He was the son of Irish immigrant parents who had first come to the USA in 1861: Patrick O'Keefe (b. 1832), a labourer, and his wife Julia (b. 1834). One of four children, his only surviving sibling was his sister Margaret (b. 1862). Two brothers, William and John, had died in early childhood.
Arthur first appears on the 1870 census living with his family at unspecified address in Rahway. His father passed away around 1880 (3) (possibly in California) and when the family appeared on the 1880 census they were living on Monroe Street, Rahway where Arthur would spend the rest of his life. Arthur was unmarried and he and his mother were still living together on Monroe Street by the time of the 1900 census, Arthur described as a grocer.
His sister was married to John Coyle O'Brien (b. 1862) in 1897 and had a daughter named Marguerite (1900-1970, later Mrs William Flanaghan). The couple ran a store in Rahway but Margaret was widowed in 1908 and returned home to live with her mother and brother Arthur. They appeared on the 1910 census living at 90 Monroe Street and the family ran their grocery store together. Their mother would pass away in 1911.
Known as Artie to his friends, O'Keefe is believed to have been a Freemason. Besides his grocery store he owned property in Rahway and was active in local politics with the Republican party, possibly earning him the monikers "The Mayor of the Bronx" and "The Mayor of East Rahway."
In February 1912 Arthur left his home for a vacation, intent on visiting England, Scotland and Ireland. At intervals he would send home postcards and gifts from the various places he visited, including some Irish shamrocks which he timed to arrive in America on St Patrick's Day (17 March). Plans had been made for the National Fife and Drum Corps of East Rahway Fraternal Section to greet O'Keefe upon his arrival back in New Jersey.
On the night of the sinking it is speculated that O'Keefe was one of the men who managed to pull themselves aboard the waterlogged Collapsible A and was the man that Norwegian passenger Olaus Abelseth tried to help. Abelseth had shared a carriage on the boat train to Southampton with a New Jersey man who he later encountered in Collapsible A, lying freezing, so he propped him up and attempted to revive him, telling him to brace himself and that a ship was coming. The man would say, "Leave me be," and "Who are you?" before he died of exposure. The body of this man was left in the boat when Fifth Officer Lowe arrived to transfer her survivors. A month after the sinking the Oceanic came across the drifting Collapsible A, the three bodies were recovered and buried at sea.