The Scots pro team went into their winner-takes-all 50-over showdown against the Seafarers with the advantage of a four-point cushion over their Dutch rivals.
And they had reduced the visitors to 145-9 with three wickets each from Aman Bailwal and Gordon Goudie before torrential rain at the Grange wiped out further play.
The Highlanders had already clinched the inaugural Pro 20 title and Michael Leask, the man-of-the-series, declared: "We've really enjoyed the new competition and are delighted to have done the double.
"It's a shame not to finish it on the field but we are obviously pleased with the outcome and I think we have deserved our success."
Reivers dodged a double wooden spoon with victory over Northern Hurricanes in Deventer.