[1] As a child, he was an active swimmer and surfer, and in 1928, Mullahey and two friends made local news for paddling on surfboards from Waimānalo to Mānana island, a distance of about 1 mile (1.6 km).

Mullahey served as an underwater demolitions expert, free diving at Wake and Midway atolls to place dynamite charges needed to clear coral to create landing channels in the lagoons.

[11] When World War II broke out, Mullahey was airport manager in Auckland, New Zealand, from where he helped evacuate Pan Am staff from across the Pacific.

[15][16] During his time with Pan Am, Mullahey oversaw development of the Boeing 314 Clipper base at Cavite Naval Yard in the Philippines, opened a base at Suva, Fiji, arranged for the first Pan Am flights to Macao and Hong Kong, and oversaw aerial and landing surveys in Fiji, Lau, and New Caledonia, as well as opened new routes to other Pacific destinations.

[11] In 1951, Mullahey set about organizing the first Pacific-area travel conference with the aim of promoting tourism to the Asia–Pacific region, which had been heavily affected by World War II.

[23] In 2007, the University of Hawaiʻi at Mānoa School of Travel Industry Management and the Hawaii Hospitality Hall of Fame posthumously honored Mullahey for his legacy.

[26] Mullahey married twice, first in 1935 to Mary H. Mason (1913–1955) of Hilo, Hawaiʻi, with whom he had a son, Michael;[10] then, in 1956, to Margaret White née Dalzell (1912–1999).