The 34-year-old former Leicester, Liverpool, Birmingham and Wigan player won 62 caps for his country, scoring seven goals and playing at two World Cups, but was without a club after being released by Villa at the end of last season.
Heskey will join former Sunderland and Leeds United forward Michael Bridges at the Jets and follows fellow former Liverpool striker Robbie Fowler, who played in the A-League for two years, in moving to Australia.
"This is an exciting new period in my life and I am looking forward to making a special contribution to the A-League and most importantly, to the Jets," Heskey said in a statement released by the club on Friday.
"I hope I can help grow football at the grassroots level and also provide advice to young players at the Jets.
"The season isn't far away, so I will be in Newcastle soon, training with my new team mates and be ready for kick off on October 7."
The club is owned by mining magnate Nathan Tinkler's Hunter Sports Group (HSG), which threatened to relinquish the franchise earlier this year after suffering an "irrevocable breakdown in confidence" in the management of Football Federation Australia (FFA).
The row was eventually resolved after direct talks between Tinkler and his fellow multi-millionaire Frank Lowy, who is chairman of the FFA and the kingpin of Australian football.
The eighth A-League season begins next month with 2007-08 champions Newcastle hosting Adelaide United on October 7 before making the short trip down the coast on October 13 to face Sydney FC and World Cup winner Del Piero.