The SPL, which had been without a sponsor since its inception, will in future be known as the Bank of Scotland Scottish Premier League, with pounds 2.25m agreed for the next two years and an option already in place for a pounds 1.5m extension for a further season.
Mitchell said: "There was no anxiety to get this deal done and there was never a concern for me [that] we might find ourselves without a sponsor. The initial contact for this deal was on day two of the season but it is a complex deal and I don't believe it could have worked out any better for us.
"It is a mistake to talk about this money on its own as we have secured pounds 70m over the next four years with significant broadcast deals. At no stage did we drop our price and we must emphasise this is the most lucrative deal which has ever come the way of the top division."
According to the SPL's own figures, last season's sponsorship arrangements with Bell's brought the SFL a sum of pounds 850,000 per season, making today's deal a modest increase of pounds 150,000 per term.
This compares poorly with the SPL's fourfold increase in broadcasting revenue, though with the Bank of Scotland there is no requirement to share the monies with all 40 Scottish clubs. Even given that, however, each team will gain around pounds 2,000 a week from the deal, which has prompted scepticism of its real value given the escalating prices of player wages and transfers.
George Mitchell, general manager of personal banking at the Bank of Scotland, said: "It is a good deal for us and a tremendous opportunity."