The SPL broke away from the Scottish Football League in 1998 but all 42 clubs will now come together again under one body after a deal for league reconstruction was agreed.
Asked if he agreed that the SPL had failed as a project to enhance the Scottish game, Doncaster said: "Not at all. Over the period of the SPL, we have seen two of our clubs reach European finals, we have seen increases in the revenue that have come into the SPL and have been paid to clubs, and we have seen the development of football in this country, so absolutely not."
He added: "It's been a very effective way of concentrating resources in the top tier. Whether that has been best for all levels of the game has been debatable.
"That's why having a single league, representing all 42 clubs is the right way forward."
All 12 top-flight clubs agreed to push ahead with plans for a single merged body last month and the scheme was rubber-stamped on Wednesday when 23 lower-league sides also gave their backing.
The so-called 'Scottish Professional Football League' will hold its first board meeting on June 27 when more details about its make-up are expected to be announced.
Doncaster's own position is due to be clarified on that date too, but the 43-year-old former Norwich executive refused to confirm whether he would throw his hat in the ring for the new set-up's top job.
"This can't be about individuals," he said. "It has to be about what is best interests for the game overall in this country. Any decisions about the future are really a matter for the new board when it sits for the first time at the end of the month."
The terms of current four-year broadcasting deal with Sky and ESPN/BT are expected to be honoured by the SPFL but a title sponsor for the top division is now an urgent necessity following the Clydesdale Bank's decision to end their six-years deal.