Josh played as an openside flanker, and his greatest attribute was considered to be the speed with which he was able to get to breakdowns in play, in order to gain or regain possession of the ball.
He was born in Hastings in Hawkes Bay, and attended Hastings Boys' High School. He played his early rugby union at scrum-half and centre, switching to flanker at high school. In 1990 Kronfeld moved to Dunedin to study physical education at the University of Otago. Here he became involved in the Otago University Rugby Club. After playing one game in 1992, Josh gained a starting position in the Otago team in the National Provincial Championship (NPC) for 1993. Josh would eventually play 69 matches for Otago.
He made his All Black test debut in 1995, playing against Canada at Eden Park in Auckland. He played in the 1995 Rugby World Cup including the final in which the All Blacks lost a thrilling game to South Africa. He also played for the Highlanders Super 12 franchise. In total, he made 42 appearances for the Highlanders.
He made five appearances in the All Blacks’ 1999 World Cup campaign, which included the game against England and the amazing semi-final with France that took place at Twickenham. Josh remained a first choice player for Otago, the Highlanders and the All Blacks until 2000. In May 2001 he officially signed with English club Leicester Tigers.
In 2003, hed returned to New Zealand, and subsequently retired from first-class rugby. He has made numerous media appearances, e.g. Celebrity Treasure Island. He has also returned to the University of Otago to study physiotherapy.
He was a participant in the 2009 TVNZ entertainment series "Dancing with the Stars".