Gregory "Greg" Henderson (born 10 September 1976) is a professional track and road racing cyclist who rides for UnitedHealthcare. His career includes winning the 15 kilometres (9.3 mi) scratch race at the 2004 world championships and, in road cycling, winning the points competition at the 2005 Tour de Georgia. He repeated this feat in 2008. During an important part of his career, he served as André Greipel's main lead-out man, and they have been colleagues at both T-Mobile Team and later Lotto–Soudal.
In 2007, he rode for T-Mobile Team. Henderson received a Bachelor of Physical Education from the University of Otago.
In addition to 17 New Zealand track and road titles and eight World Cup track golds, Henderson has been New Zealand Track Cyclist of the Year (2001, 2002, 2003) and Athlete of the Year, Otago, New Zealand (2001, 2002, 2003).
At the 1998 Commonwealth Games Henderson won bronze medals in the 40 km points race and the 4000 m team pursuit.
He won gold in the 40 km points race and bronze again in the 4000 m team pursuit at the 2002 Commonwealth Games.
He won the 15km scratch race at the 2004 world championships.
At the 2004 Summer Olympics he finished fourth in the points race and seventh in the madison.
His best placing in the 2006 Commonwealth Games was 10th in the scratch race.
At the 2008 Summer Olympics he finished tenth in the points race and the madison.
In 2005, he won the points competition at the Tour de Georgia and International Tour de 'Toona. In 2006, he from early injuries and won the inaugural Pro Cycling Tour (PCT) Reading Classic.
In 2009, he won the Clásica de Almería in Spain, the second stage of Vuelta Ciclista a Murcia, and the third stage of the Vuelta a España.
In 2010, he won the first stage of the Paris–Nice. In 2011, he won stage 2 of Paris–Nice and stage 3 of the Tour of California.
Henderson left Team Sky at the end of 2011, and joined Lotto–Belisol, mainly to act as lead-out man for Andre Greipel. In April 2015, he expressed his opinion on Twitter that Fabio Aru of rival team Astana missed the Giro del Trentino not because of illness as it was announced, but because he had an ongoing investigation into his biological passport for doping. Henderson apologised shortly after. He competed in the 2016 Tour de France.
He is married to the Australian cyclist Katie Mactier.