Verstappen has won two races this season; the first one coming in a thrilling Austrian Grand Prix - overtaking Charles Leclerc with a few laps remaining - and his second coming at a soaking wet Hockenheimring in one of the more bizarre races of the season.
"As a driver, he is complete and ready for the championship," Marko said to Motorsport.com. "If we give him the right material, then he will become that too. An example is the GP at the Hockenheimring: We managed to go so much faster than the rest. That is what we have become more or less used to from him in Formula 1.
"We saw similar skills in the rain in Formula 3, and we took the risk of bringing him in at a young age. That now pays off."
Verstappen, despite having a strong season, is too far behind Lewis Hamilton at the top to mount a real title challenge in 2019, but Marko believes in the near-future, the 21-year-old will be able to compete for the world championship.
"If a driver becomes more routine, he will also become faster, ask less of the tyres and load the engine less," Marko said. "His speed is good, only more is coming! He managed to get the most out of the car every race, even if a win was not possible. Let us not forget that he will soon turn 22 (September 30)."