A “pitmaster” (or “pit master”) is the chef of a barbecue pit. The term “barbecue pit master” has been cited in print since at least 1961, but “pitmaster” began to be frequently used since only the 1980s.
 
Robb Walsh’s book, Legends of Texas barbecue: recipes and recollections from the pit masters (2002), was the first time that “pit master” appeared in a book title.
   
   
Wiktionary: pitmaster
Etymology
pit +‎ master
Noun
pitmaster (plural pitmasters)
1. One who operates a barbecue pit. Sometimes a term of respect for someone who is skilled at barbecuing.
         
19 May 1961, Traverse City (MI) Record-Eagle, “Prepare Mountains of Food for NMC Barbecue Sunday,” pg. 1, col. 2:
Andy Olson, barbecue pit master who annually supervises the barbecuing of the meat, will again give of his talents to assure a savory and succulent main dish.
 
6 May 1964, Eureka=Humbolt (CA) Standard, “Annual Barbecue, Rodeo Of Sheriff’s Mounted Posse Set At Fortuna This Sunday,” pg. 3, col. 4:
Chef for the barbecue will be veteran pit-master A. L. “Blackie” Beers, county jail farm steward.
 
16 September 1968, Newark (PH) Advocate, “Barbecue-On-The-Square Set,” pg. 1, cols. 7-8:
Harley B. Oiler and Robert L. Greenwall will be barbecue pit masters Sunday while Jaycee sub-chairmen are Mike Cherubini, Jack Dougherty, Howard Hopkins, Glenn F. Abel, Dave Riley, and Ron Braschler.
     
Google Books
Roadfood
By Jane Stern and Michael Stern
New York, NY: Random House
1980
Pg. 4:
In Texas it might be the hidden-away barbecue pit on the back room of a general store where an elderly pitmaster smokes the best hot links in the state;...
 
Google Books
December 1983, Texas Monthly, pg. 253, col. 1:
The Germans in particular fell hard for the romance of Texas beef, setting up the premier meat markets and turning themselves into such superb barbecue pitmasters that sauce was (and still is) beside the point.
     
Google Books
The interstate gourmet—Texas and the Southwest
By Barbara Rodriguez, Tom Miller, Neal O. Weiner and David M. Schwartz
New York, NY: Summit Books
1986
Pg. 99:
Every time she runs across brisket nearly as good, it turns out that the pit master learned his trade from Angelo.
 
22 June 1988, St. Paul (MN) Pioneer Press, “Barbecue Debate—Sauce’s secret ingredient is strong opinion,” pg. 1B:
Noun, verb, adjective - “barbecue” ays is all. But when people in Texas and Kansas discuss barbecue, they’re not speaking the same lingo. Worse yet, pit masters in western and eastern North Carolina interpret barbecue so differently that the debate still hasn’t been settled.
 
24 July 1991, Augusta (GA) Chronicle, “Barbecue contest,” pg. B1, col. 1:
“Here’s the chance for all those folks who brag about their berbecue expertise to show off,” says Frank Frog Bobo, “pitmaster of ceremonies” for the event.
   
OCLC WorldCat record
Legends of Texas barbecue : recipes and recollections from the pit masters
Author: Robb Walsh
Publisher: San Francisco, Calif. : Chronicle ; Andover : Ragged Bears, 2002.
Edition/Format: Book : English
 
OCLC WorldCat record
Barbecue road trip : recipes, restaurants, & pitmasters from America’s great barbecue
Author: Michael Karl Witzel
Publisher: Minneapolis, Minn. : Voyageur Press, 2008.
Edition/Format: Book : English
 
OCLC WorldCat record
INSIDE THE CULT OF ‘CUE - The pitmasters of Austin offer some lessons learned from the long-lived dining traditions in Austin’s Barbecue Belt.
Author: Craig Goldwyn
Publisher: [Cleveland, Ohio : Penton/IPC]
Edition/Format: Article : English
Publication: Restaurant hospitality. 92, no. 7, (2008): 32
Database: ArticleFirst