Fusing conditional write instructions having opposite conditions in instruction processing circuits and related processor systems, methods, and computer-readable media are disclosed. In one embodiment, a first conditional write instruction writing a first value to a target register based on evaluating a first condition is detected by an instruction processing circuit. The circuit also detects a second conditional write instruction writing a second value to the target register based on evaluating a second condition that is a logical opposite of the first condition. Either the first condition or the second condition is selected as a fused instruction condition, and corresponding values are selected as if-true and if-false values. A fused instruction is generated for selectively writing the if-true value to the target register if the fused instruction condition evaluates to true, and selectively writing the if-false value to the target register if the fused instruction condition evaluates to false.