The arrest is a major breakthrough for police investigating a string of bloody underworld shootings across Sydney in recent years.
Assaad was gunned down in broad daylight while standing in the driveway of his Georges Hall home in Sydney's southwest in October.
The 29-year-old was getting into his car when he was allegedly shot multiple times by two men who sped off in a black Audi sports car which was found burnt out at a park three days later.
Assaad was a key suspect in the April 2016 murder of underworld kingpin and convicted killer Walid Ahmad who was gunned down at a Bankstown shopping centre.
A suspect in Assaad's murder, 29-year-old Kemal Barakat, was killed in his Mortlake apartment in March this year.
Ten gangland figures have been killed in Sydney since 2015.
- AAP