Vettel wrapped up back-to-back titles in October with four grands prix to spare, ultimately becoming the youngest double champion in F1 history by 122 points, virtually the equivalent of five race victories.
Whitmarsh, however, believes the competitive nature of the sport means Red Bull star Vettel will not have it all his own way this year.
With six world champions on the grid for the first time in F1 - Vettel, McLaren duo Lewis Hamilton and Jenson Button, Fernando Alonso, Michael Schumacher and Kimi Raikkonen - Whitmarsh said: "It will be close.
"It's a massively competitive championship these days. There's no doubt about that.
"No one, in my view, is going to run away with this victory, not us, not anyone else."
Whitmarsh is convinced, however, McLaren will be in the hunt to the end this year, unlike last season when they and every other team were trounced by Red Bull.
Despite six grands prix wins - split equally between Hamilton and Button - for the most part McLaren were no match for Vettel who won 11 races and was on pole a record-breaking 15 times.
As for the constructors' championship, McLaren finished 153 points adrift of Red Bull.
Yet despite only taking the wraps off his team's new car on Wednesday, Whitmarsh has no doubts his drivers will be in the hunt throughout the 20-race campaign, providing they set off on the right foot.
That was not the case a year ago when McLaren endured what Whitmarsh has described as "an abysmal winter testing session" due to fundamental mistakes made in development.
On this occasion Whitmarsh said: "With the way the development has happened, we're finding good performance.
"We've set ourselves some tough targets which, if achieved, will allow us to win the world championship.
"We haven't reached those targets yet, but fortunately we're not at the first race. The progress and trend is towards meeting them.
"We've our engineers who have to have their own moments of inspiration, and they've got to develop and work hard to make this car competitive.
"And it's not just about testing, it's not about the first race.
"You have to improve the car through every single race throughout a season to sustain a championship campaign these days.
"That's something I think we're quite good at, and providing we have a good and competitive start to the year, then there's no doubt we'll be in the fight for the championship at the end."