But his life changed in 2002, when he was jailed by the Egyptians. During his time in prison, his ideas were deeply challenged, and in the end he decided to leave HT.
Having played a significant role in bringing about a shift to extremism, he said he felt a responsibility to use his experience and knowledge to try to reverse that work.
"It's a very difficult thing to do, but when I first started this I thought if we don't do it, who the hell is going to?" Nawaz told AlertNet. "This opportunity only comes around once every so often when you've got someone who's got that experience and who knows the Islamist arguments and is able to put them forward and then critique them.
"Bit of a burden," he said with a laugh.
In 2010, he founded Khudi, the first social movement in Pakistan to challenge extremist religious ideas and instead promote democratic culture among the country's youths.
Its aim is to spread democratic values in every area of Pakistani life as its members become journalists, judges, politicians, and activists.
"It's a very grandiose and long-term ambition, but already we're beginning to see fruits," he said.
Tens of thousands follow Khudi on social media. They've organized national and international conferences, and local television station Express News TV is airing a series of debates on extremism.