[6] [7] O'Brien grew up in South Bend, Indiana until age ten, then Phoenix, Arizona for two years before moving to Toledo, Ohio where he attended St. John's High School.
[10] O'Brien took a second Freeman scholarship in France while also working at United States Bureau of Foreign and Domestic Commerce office in with the American legation in Stockholm.
In 1928, O'Brien returned from studies in Europe and accepted an assistant professorship of mechanical engineering at University of California, Berkeley.
[14] In 1950 O'Brien was one of the "Committee of Seven" opposing Regent John Francis Neylan's call to fire any faculty refusing to sign a loyalty oath meant to target communist sympathizers.
[22] 12 linear feet of O'Brien's documents are archived in University of California, Riverside's Water Resources Collection.
O'Brien continued to serve as a member of the Beach Erosion Board and beyond 1963, its successor organization, the Coastal Engineering Research Center until his retirement in 1978.
[30] [21] In light of the difficult amphibious landings during the Battle of Tarawa, O'Brien along with other colleagues at Berkeley as well as H. U. Sverdrup developed a method of determining the depth of coastal water based on the height of the ocean waves.
[32] O'Brien also had a long career as a technical consultant to General Electric, particularly their aerospace division, where he contributed to the development of axial-flow jet engines.