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After struggling with serious back and shoulder injuries in recent times, the 34-year-old has decided to focus on a new role as an insurance specialist in Auckland.
It ends a career in which he won bronze in the javelin at the Rio Paralympics in 2016.
A year earlier he won silver at the world championships, setting the New Zealand F44 record of 55.80m in the process.
However, given his injuries, he felt it was time to look to the future.
"My retirement coincided with a job offer and reflecting on what I’d achieved across 10 years of javelin-throwing I was quite happy. I’d enjoyed a good career.
"I’d had a few big injuries over the last few years and I felt it was a bridge too far to carry on to Tokyo, so I felt it was the right time to make a clean break."
McSweeney had been struck by a truck at age 3, resulting in the amputation of his left leg below the knee.
He continued to play sport and underwent more than a dozen surgeries in order to reduce the size of his tibia bone.
After leaving school he tried various odd jobs, but suffered from chronic depression and his life unravelled.
He dropped out of university three years in a row, started using drugs and was arrested.
However, he worked his way back and after reading of a 2009 Paralympics training camp, he decided to give it a go.
"Taking up athletics was a big turning point for me," he said.
"For the first time in my life I had something I could focus on and that I could look forward to. I knew it was my path."
Six months later he moved to Dunedin to be coached by Raylene Bates.
She taught him the basics of becoming a serious and committed athlete and in 2011 McSweeney made his international debut.
Many successes followed.
However, he picked up a back injury the day before he flew to Rio — later diagnosed as a bone stress problem.
To perform as he did in Rio under those circumstances, he said, "was massive".