The playmaker's career began with OFI Crete FC in 1982, where he remained for a decade, winning the Greek Cup in 1987. He then moved to Panathinaikos FC. In his first season with the greens, he won the cup again and, in 1994/95, the domestic double. The next season the Athens side retained the title and Nioplias played a vital role in their run to the UEFA Champions League semi-finals. In 1996 he returned to OFI and remained there for six seasons until a move to Halkidona FC, a newly-promoted side. There, he ended his career in the Summer of 2004, having racked up 509 Greek top-flight appearances, second only to Mimis Domazos - 363 appearances with OFI FC.
Meanwhile, he carved out a distinguished international career. Playing for Greece at the 1984 UEFA European Under-18 Championship finals, four years later he helped his nation to the final of the UEFA European U21 Championship. He graduated to the senior team, and was in the squad that qualified for the 1994 FIFA World Cup. In all he won 44 caps, and his move into coaching was no surprise as he was considered a natural instructor even on the pitch.
After gaining a diploma in the Netherlands, in January 2005 he gained his first coaching role: Coach of the Under 19 Greek national football team. He proved an immediate success as he masterminded Greece's progress to these finals in late May with wins against Scotland, Austria and Slovakia. In the latter game, when Greece only needed a point, he played an attacking game for a 2-0 victory and explained: "We played to win, because we must never allow expedience to come into the picture for such young players. Football should be joyful and that's the idea we are trying to instill in them."
In 2007, Nioplias became coach of the Under-21 National Football Team of Greece. On December 8, 2009, he was selected to replace Henk ten Cate as coach of Panathinaikos. Nioplias responded by winning the league title but was sacked the following season after a string of disappointing results.