Nadeem won the men's gold on day 7 with a new event record distance of 86.29 metres.
With the Olympic qualification standard set at 85 metres, it was enough to also confirm his place at the Games in 2020.
The 22-year-old competed at the Doha 2019 IAAF World Championships and is the first Pakistani track and field athlete to achieve direct qualification for an Olympics since before he was born.
Second place went to India’s Shivpal Singh, who endured a below-par outing at the 2019 IAAF World Championships. He threw a distance of 84.43 metres in Nepal, just outside Tokyo 2020 qualification.
Despite that disappointment, the athletics federation of India responded to the success of their neighbours on social media, and received plaudits for their sportsmanship online.
On twitter they posted "Congrats #ArshadNadeem, javelin star of #Pakistan for winning gold at #SAGames2019 with a throw of 86.48m (PB & New Pakistani record). Qualified for #Tokyo2020 Olympics, first Pakistani athlete in decades to earn direct qualification."
The post was accompanied by a photo of Nadeem at the 2018 Asian Games, shaking hands with India's Neeraj Chopra, who previously held the record.