Detectives arrested the man at Sydney International Airport about 3.30pm on Sunday.
Police said the man was "attempting to flee the country".
The man has been taken to Surry Hills Police Station where he is assisting police with their inquiries into the death of Taha Sabbagh.
Mr Sabbagh was shot last month while sitting in a car with his son in what police described as a callous, gangland-style killing.
The 40-year-old father was outside the Elite Fight Force mixed martial arts gym in Sefton just after 6.30am on March 2 when he was shot multiple times in the chest, police said.
Despite the efforts of NSW Ambulance paramedics, Mr Sabbagh died at the scene.
His 12-year-old son, who was in the passenger seat of the vehicle at the time, was physically unharmed.
Police later found a burnt-out Mazda 3 about a kilometre away in neighbouring Birrong.
Detective Superintendent Danny Doherty described the murder as an "egregious, violent act".
"These people are callous and brazen," he told reporters at the time.
"They have no regard for human life knowing there was a 12-year-old boy in the car and still carrying out the execution in front of him."
Investigations under Strike Force Pemak are continuing.
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