Conker's Bad Fur Day is an action-platform game where the player controls Conker the Squirrel through several levels. The game also features an overworld in which the player can transition from one level to another, although many of which are initially blocked off until Conker earns a certain amount of cash. Each level is an enclosed area in which the player can freely explore in order to encounter tasks to do. The gameplay mostly relies on figuring out a way to help several characters by completing a linear sequence of challenges. These challenges may include defeating a boss, solving puzzles, gathering objects and racing opponents, among others. The result is always a cash reward, which aids access to other areas in the overworld.
Conker's abilities are far simpler than those of previous Rare platformers, such as Banjo-Kazooie or Donkey Kong 64. The player can run, jump, and smack enemies with a frying pan. Besides this, he also has few other physical abilities. He can swim underwater for a while until he runs out of breath, climb ladders or ropes, and is strong enough to push heavy objects. To regain lost health, Conker can eat pieces of "Anti-Gravity" Chocolate that are scattered throughout the levels. Additionally, the game employs "context sensitive" pads that allow Conker to gain different, temporary abilities when pressing the "B" button atop them. For instance, in the beginning of the game, by pressing the B button on the first pad he encounters, Conker drinks some Alka-Seltzer to wipe out his hangover, at which point players can proceed forward. Some pads can turn Conker into an anvil in order to slam into the ground, and some are also used to pull out his shotgun, to activate his throwing knives, slingshot and so on.
Conker's Bad Fur Day follows the story of Conker the Squirrel, a red squirrel, who finds himself lost in a strange land after a night of binge drinking with his friends, and embarks on a quest simply to return home to his girlfriend, Berri. Meanwhile, the Panther King, ruler of the land that Conker is lost in, finds that his throne's side table is missing one of its legs and orders his quadriplegic weasel servant, Professor Von Kriplespac, to solve the problem. Kriplespac suggests the use of a red squirrel as the fourth leg for his table, and therefore the Panther King sends his minions to search for one and capture it. As Conker searches for his way home, he finds himself embroiled in a series of increasingly absurd and often dangerous situations, including having to recover a bee hive from some enormous wasps, confronting a giant opera-singing pile of feces, being turned into a bat by a vampire, and even getting drafted into a war between grey squirrels and a Nazi-like group of teddy bears known as the "Tediz," which Conker ultimately destroys. During his quest to return home, Conker finds wads of cash scattered throughout the land and becomes sidetracked from his goal.
In the final chapter of the game, Conker and Berri are enlisted by Don Weaso, head of the weasel mafia, to rob a bank. After entering the vault, they find that the bank scene was an elaborate trap set by the King and Don Weaso to capture Conker. In the ensuing confrontation, Berri is killed by Weaso. Afterwards, a Xenomorph suddenly bursts out of the Panther King's chest, killing him instantly. Von Kriplespac explains that the alien is one of his creations and that he had planned to use this opportunity to kill the King and escape captivity. Kriplespac then reveals that they are all actually inside a spaceship, which he activates and takes into low orbit. From there, he instructs the alien to attack and kill Conker as revenge for destroying the Tediz, which were also his creations. Conker pulls a switch that opens an air lock, pulling Von Kriplespac and Berri's corpse into space. After Conker briefly battles the alien with the aid of a robotic suit, the alien takes one last lunge at him, when suddenly the entire game freezes. Conker expresses disbelief that the developers of the game apparently did not beta test the game properly, and breaks the fourth wall to ask some software engineers to assist him in his current situation. The programmers give Conker a Katana and teleport him to the Panther King's throne room, where he decapitates the alien. As a result, he is crowned the new King of the land.
Conker then comes to the grim realisation that Berri is still dead. He attempts to ask the programmers to bring her back to life, but realizes that they have already left. Conker then gives a closing monologue, in which he discusses appreciating what one already has instead of always wanting more, stating that "the grass is always greener, and you don't really know what it is you have until it's gone." The credits roll, and afterwards Conker is seen back at the same pub he was seen in at the start of the game, drowning his sorrows in Scotch whisky. He drunkenly exits the bar as it begins to storm outside, and leaves in the direction opposite the one he took previously.