Hamilton won the season-closing Abu Dhabi Grand Prix on Sunday to clinch his second drivers' crown, finishing 67 points clear of Mercedes team-mate and championship runner-up Nico Rosberg.
However, Stewart - the last Briton to become a double world champion before Hamilton - has urged caution in assessing the 29-year-old's career achievements too soon.
"Much too early to say [if Hamilton is a great]," he told Perform. "You can't judge that for another 10 years.
"If you're going to be inducted into the hall of fame or the greatest drivers in the world... it's got to be 20-30 years after your retirement that you would be inducted, so that you see what really is happening.
"I don't think you can ever say that after a world championship. [Michael] Schumacher has won seven of them, Alain Prost won four, [Juan Manuel] Fangio won five, I won three, [Nelson] Piquet won three, [Jack] Brabham won three - you just can't do it that way.
"Jim Clark only won two world championships, but he is one of the great drivers in the world, so it's far too early to say that Lewis or Nico could be one of the great drivers of all time.
"Here, we're looking at Sebastian Vettel who's won four world championships. No one's paying an attention to him, right now. So the 'great' issue is very papier mache."
Hamilton, who also won the crown in 2008, has indicated a desire to agree a long-term stay at Mercedes, with one year to run on his current deal.