Wolfenstein: The Old Blood is a standalone expansion to 2014's Wolfenstein: The New Order. Players once again step into the shoes of Polish-American OSA Operative William "B.J." Blazkowicz, this time in a prequel to the events that kick off the original games plot. The year is 1946 and the Allies are losing the war to the Nazis due to the technological superiority afforded to the Nazis by one General Wilhelm Strasse. He is more commonly known by his alias "Deathshead", a scientific genius who is developing great and terrible technology that could cripple the Allies once and for all. In order to have any chance of defeating Deathshead, the allies must first find the location of Deathshead's hidden compound to strike at the source. However the location of Deathshead's compound is known by only one other member of the Reich: SS Paranormal division leader Helga Von Schabbs, a mad woman who has sequestered herself in the massive and notorious Castle Wolfenstein. Thus B.J. is sent in to infiltrate Castle Wolfenstein and find the location of Deathshead's base, as well as learn of the dark secrets surrounding the castle itself while also coming face to face with the ferocious thug Rudi Jäger.

The game plays almost identically to The New Order, meaning that the game features a blend of stealth action as well as fast-paced and brutal first-person combat. Players can switch freely between play styles to suit how they wish to play through the game. There is a traditional health and armor meter, with only 20 points of health regenerating at a time rather than regaining a full bar of health. Health can also be overcharged by consuming medkits when at full health, however this overcharge is only temporary and should be used smartly and sparingly. Armor can be scavenged from the corpses of foes as well as found in the many hidden nooks and crannies in the game which also hides treasures and other goodies throughout the levels. Combat is carried out with numerous modified takes on historical weapons, as well as some experimental. Most of them can also be dual wielded by the player for extra power but decreased accuracy. New to the game are the pipes, which replace the knives and allow B.J. to tamper with more electrical devices as well as climbing certain walls. The game includes a simple, context sensitive cover system which simply allows a player to hide behind cover automatically when crouching or taking spot behind a sufficient piece of cover and leaning in and out to fire.

New to this game are the challenges, small portions of the game that are unlocked as you play through the campaign which allow you to take on specific mini-challenges and survive numerous foes in order to obtain a high score.