DeGale is aiming to become the first boxer from the UK to add a professional world championship to an Olympic Gold medal.
The 29-year-old Londoner finished on top of the podium at the 2008 Beijing Games in the middleweight category, four years on from Dirrell scooping bronze in the same weight class.
This pedigree has transferred effectively to the paid ranks, with both men nursing a solitary defeat apiece since turning over – although a major world belt has eluded them until now.
“It’s going to be very, very technical,” DeGale told World Boxing News. “The skill level in the fight is going to be very high.
“We’re both Olympians – I’m a gold medalist from 2008, he’s a bronze medalist from 2004.
“We both believe in our ability. We both think we’re the best. That’s why it’s going to be such a good fight.
“There’s a world title on the line, we’re both ambitious and confident in our ability.”
Dirrell’s younger brother Anthony Dirrell collected the WBC super-middleweight crown against Sakio Bika in December 2013.
Anthony was poised for a showdown with DeGale’s bitter domestic rival George Groves later this year before suffering a surprise loss to Badou Jack in Las Vegas last month.
That setback adds weight to DeGale’s assertion that he is tackling the more talented sibling, a man he believes was harshly treated by the ringside judges when he dropped a split decision to Carl Froch on his previous world-title bid.
“I’ve definitely got the best brother,” DeGale added. “Just look at his amateur pedigree – look at his fights, look who he’s beaten.
“Really he should be unbeaten because he beat Carl Froch.
“He’s technically better, he’s just a better all-round fighter I think.”
Follow Dom Farrell on Twitter @DomFarrell1986