The 23-year-old left the villa last month for “personal reasons” and has now opened up about living with the spectrum condition, which affects the way people see, hear and feel the world around them.
In a lengthy post on Instagram, Niall wrote: “Right, so here it goes…for this post I am putting my laying it on thick brush down and hoping to hit the nation with a love potion.
“For far too long I have suffered in silence and not acknowledged a massive fact about my life which going into the villa has led me to finally realise and accept.”
He revealed he was diagnosed as a young child but chose never to share his condition outside of his close family.
“Growing up was extremely difficult for me and I often felt out of place,” he said. “I always felt that people didn’t understand me, yet I was afraid to reveal my true scales as I did not want the label or stigma that was attached to it.
“But now I think it is important that I come forward, not only so that I can finally be honest with myself and to those around me, but also so that other individuals in my position can embrace their true colours.”
He continued: “It’s not been an easy ride for me to come to terms with this fact but I am glad that I can now accept who I am, and am looking forward to my next chapter.
“I would just like to thank the team at ITV for always backing me and giving me the opportunity to rid my myself of my insecurities and embrace the fact that I am different yet I am still a rainbow fish.
“I can’t explain how grateful I am for the support from the whole team over this period.I would also like to thank the British public for the love you have all shown me over the past few weeks, it has been overwhelming.
“Now it’s time for this rainbow fish to dive deep into the big blue ocean and show the world what I’m all about – there’s more layers to come.”
Niall finished off with the hashtags: “AutismAwareness #BeYourOwnKindOfRainbowFish #LessPrangMoreLove.”
Niall was coupled with Georgia Steel prior to his departure from the villa, which came just nine days into the series.
‘Love Island’ continues tonight at 9pm on ITV2.