Dalziel began racing in 1999 in Formula Vauxhall in Britain before progressing through British Formula Renault and British Formula 3. He relocated to the United States, where he spent three seasons (2002–2004) in the Toyota Atlantic Championship, finishing runner-up twice. He also made a single Champ Car appearance at Toronto for Dale Coyne Racing, finishing ninth.
Dalziel moved into the American Le Mans Series in 2005. From 2006 onward, he competed in the Rolex Sports Car Series, initially in Daytona Prototypes. He returned to the Champ Car World Series in 2007 with Pacific Coast Motorsports before the team released him with two races remaining. His best Champ Car result was seventh at Toronto.
In 2009, Dalziel was drawn into a legal dispute after teammate Henri Zogaib was investigated for operating a Ponzi scheme that allegedly defrauded Dalziel and his father of US$550,000. Dalziel won his legal judgment in May 2009 for US$608,000.
Dalziel's breakthrough came at the 2010 Rolex 24 at Daytona, where he co-drove a Porsche Riley for Action Express Racing alongside Terry Borcheller, João Barbosa, and Mike Rockenfeller to take the overall victory. He then moved to Starworks Motorsports for full-time competition.
The 2012 season marked Dalziel's most decorated year. At the 24 Hours of Le Mans, driving the Starworks Motorsport HPD ARX-03b in the LMP2 class alongside Enzo Potolicchio and Tom Kimber-Smith, he claimed class victory and contributed to the LMP2 teams championship. Earlier in the year at the 12 Hours of Sebring, he finished third overall and first in the WEC LMP2 class with Potolicchio and Stéphane Sarrazin. At the 24 Hours of Daytona, he qualified on pole with Starworks in the Daytona Prototype class and finished second. He also secured six Rolex Sports Car Series podiums that season, finishing runner-up in the Daytona Prototype drivers championship.
In 2014, Dalziel joined Extreme Speed Motorsports (ESM) to compete in the new IMSA United SportsCar Championship in the Prototype class alongside Scott Sharp. He also drove an Effort Porsche 911 GT3 in the Pirelli World Challenge late in the season, winning twice in six starts.
Dalziel remained with ESM in 2015, shifting focus to the FIA World Endurance Championship. He finished seventh in the standings with David Heinemeier Hansson as third driver. In the Pirelli World Challenge, he claimed two wins and ten podiums from 17 races, finishing third in the standings. In 2016, he continued with ESM in the WEC while also entering the IMSA SportsCar Championship with VisitFlorida Racing in a Corvette DP for most rounds.
Ryan Dalziel represents a generation of British drivers who found their greatest success in North American endurance and prototype racing. His 2010 Daytona win and 2012 Le Mans LMP2 victory place him among the notable Scottish contributors to international sports car racing. His career demonstrated adaptability across open-wheel, Daytona Prototype, LMP2, and GT machinery over more than fifteen years of professional competition.