Educated at Coleshill Secondary Modern School, Llanelli, Derek Quinnell first played for Llanelli RFC in 1967 and made his international debut for Wales against France in 1972. He captained Llanelli in 1979–80 and went on three British and Irish Lions tours. He was the only player in the Lions squad not to have been capped by his country when he went on the tour to New Zealand in 1971, playing in one test. He went to New Zealand again in 1977, playing in two tests, and finally to South Africa in 1980, again playing in two tests.
Remarkably, his three sons, Scott, Craig and Gavin went on to play top-flight professional rugby, with Craig winning caps for Wales in rugby union and Scott earning Wales caps in both union and league.
Derek's youngest son, Gavin, played professionally for the Magners League side Scarlets before an injury suffered in an October 2010 match between Llanelli RFC and Cross Keys cost him the sight in his left eye.