MacDowall began his motorsport career in the T Cars in 2005, where he also drove in 2006. In 2007 he switched to the British Renault Clio Cup, where he was for the 32nd team Total Control Racing. Also, he took part in the winter Championship of the Clio Cup, which he ended as third. In 2008 he improved himself in the head to seventh place and finished the Championship winter Championship again as the third. In 2009 he won four victories in the main Championship, leaving him behind Phil Glew finished second.
MacDowall's performance in the Clio Cup impressed on top teams in the BTCC, whereby he tests got at Motor base Performance, RML and West Surrey Racing. In March 2010 was then known that he was in a Chevrolet Cruze drive for RML. In the third race weekend at Brands Hatch he obtained his first podium finish by a third place in the second race. In the sixth race weekend at the Snetterton Motor Racing Circuit , he became the youngest ever polesitter in the BTCC, but he won not by gearbox problems. In the eighth race weekend at the Knockhill racing circuit Racing Circuit he achieved another podium finish with a second place in race 1. As a result, he finished eleventh in the Championship with 83 points.
In 2011 the BTCC driving for Chevrolet in MacDowall. Thanks in part to three podium finishes, he finished ninth in the Championship with 100 points.
In February 2012, it was announced that MacDowall in 2012 went riding in the World Touring Car Championship for bamboo-engineering in addition to Pasquale di Sabatino. In the final race of the Championship at the Circuito da Guia , he obtained the pole position for race 2, but he fell out in this race. Despite this, he finished eleventh in the drivers ' Championship and fourth in the independents ' trophy.
MacDowall remained for Bamboo drive in 2013, with James Nash as his new teammate. In the first race of the season at the Autodromo Nazionale Monza , he obtained his first WTCC podium with a third place. Later he obtained on the Hungaroring and Suzuka. With two meetings to go, he is 11th in the drivers ' Championship and third in the independents ' trophy.