The former Socceroos captain will replace Tony Walmsley, who was sacked after just 18 months in the Mariners' top job.
The Gosford-based club has yet to officially announce the appointment of Okon but it is believed he will start in the job as early as next week.
During a storied playing career Okon won 28 Socceroos caps and had stints with clubs in Belgium, Italy and England before winning the A-League with Newcastle Jets in his final season as a professional.
The 44-year-old soon moved into coaching, taking over the Australia Under-18 job in 2009 and being appointed Australia Under-20 manger in 2012.
Okon has also served as an assistant coach to Miron Bleiberg at Gold Coast United.
