At 8-under-par 136, the duo leads outright by a stroke over Englands Paul Casey (66) and by two over Jamie Spence (70) and Nicolas VanHootengem (66).
While Coltart is in search of his second win on the European Tour, Dredge is still looking for his first, his best finish coming in a tie for sixth at last seasons Murphys Irish Open.
The recently-turned 28-year-old may just find it this week. His play Friday at De Vere Slaley Hall came in fine form, and included six birdies, offset by a lone bogey at his last hole of the day.
Its a bit annoying to finish like that, admitted the Welshman. My second shot just pitched a few yards short of the green and rolled back and I hit a poor chip to 12 feet ' but thats the way it goes sometimes.
Of his prospects of a possible inaugural victory, Dredge commented: I wouldnt say Im going to win it, but I will certainly go for it over the weekend.
His best finish for this season is a tie for 13th, which came in Januarys Alfred Dunhill Championship. More recently, he finished 24th in Mays Moroccan Open.
One of the days highlights came by way of Australian Richard Green, who shot a new course record at Slaley Hall Friday. His 64 ousted the previous record by a shot and propelled him into a tie for sixth at minus-five.
Unfortunately for defending champion Lee Westwood, the day was not quite so kind.
Following Thursdays horrendous round of 81 ' which included three double bogies ' the big Englishman could do no better than 74 on Friday. At 11-under for the two days, he missed the cut by eight strokes.
Full-field scores from the Great North Open