Habitational name from Hackney in Greater London, named from an Old English personal name Haca (genitive Hacan) combined with ēg "island, dry ground in marshland".
From Middle English hakenei (Old French haquenée), an ambling horse, especially one considered suitable for women to ride; perhaps therefore a metonymic occupational name for a stablehand. This surname has also been found in Scotland since medieval times.