Glamorgan earned their success with a run of three successive wins in May, over Kent, Northants and Middlesex, followed by the double over Kent in July and victory away to Lancashire in August.
Derbyshire needed bright skies on the fourth morning to have any chance of forcing a win or gaining more bonus points to take the race into the final week of the season.
But further rain during the morning led umpires Steve O’Shaughnessy and Suri Shanmugam to call play off at 12:20 BST.
Glamorgan coach Richard Dawson told BBC Sport Wales:
“We’re waiting on a few games, so we’ll keep an eye on the scores during the bus journey back.
“It’s been a bizarre four days with the first day out because of the winds, then the rain. I thought we did really well batting in the circumstances and the conditions, Kiran’s innings was outstanding, but a weird four days.
“When Derbyshire came to Cardiff (in early May) and we nearly got over the line, it changed the mindset especially at home. We could score runs and take wickets at home to force victories, on the back of that we got on a bit of a roll and people put in match-winning performance, so Derbyshire in Cardiff was the turning point.”
Derbyshire head of cricket Mickey Arthur told BBC Sport Wales:
“It’s been very disappointing, it was going to be a good game between two very good teams but it is September in the UK and we’ve had a good summer.
“Kiran Carlson played really well, he took the attack back to us and played in an unconventional way.
“We’re an ambitious squad and I never allow us just to go through the motions. Third is better than fourth so we’ve got to make sure that when we come back from (the final game at) Kent we’re third in our division.
“if we do that, considering where we were this time last year, we’ve made steady progress.”
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