Having won Nissan's GT Academy online competition in 2011, which included an on-track race at Silverstone, Mardenborough entered the world of motorsports.
Competing in sportscars, he went on to contest Formula 3 with Carlin where he finished sixth in the British Formula Three Championship.
His efforts caught the attention of Red Bull team boss Horner who will now race the 22-year-old in his Arden International team in GP3.
"I feel ready for GP3," he said. "I've prepared well and I have all the right people around me to help my development, so I can fully focus on my racing.
"I haven't raced the GP3 car yet but, going on initial testing, I prefer the GP3 car to an F3 car. The power is very addictive! This season is my opportunity to impress more people in the sport who make the decisions on who makes it into F1 and who doesn't and I'm going to give it my best shot.
"F3 has taught me so many things, both in the car and out of the car, both mentally and physically. It was a great stage in my development and I'm sure the skills I've learnt there will help me in GP3 and beyond."
However, Mardenborough is already looking to the future and told Sky Sports Online that he dreams of Formula One.
"That will be the ultimate goal, but we are just trying to see how far we can go up the ladder and see if I can keep improving. If I keep improving then I think that is possible," he said.