With the advent of nanometer technology, circuits are more prone to transient faults that can occur during its operation. Of the different types of transient faults reported in the literature, the single-event upset (SEU) is prominent. Traditional techniques such as triple-modular redundancy (TMR) consume large area and power. Reversible logic has been gaining interest in the recent past due to its less heat dissipation characteristics. This paper proposes the following: 1, a novel universal reversible logic gate (URG) and a set of basic sequential elements that could be used for building reversible sequential circuits, with 25% less garbage than the best reported in the literature; (2) a reversible gate that can mimic the functionality of a lookup table (LUT) that can be used to construct a reversible field-programmable gate array (FPGA); and (3) automatic conversion of any given reversible circuit into an online testable circuit that can detect online any single-bit errors, including soft errors in the logic blocks, using theoretically proved minimum garbage, which is significantly lesser than the best reported in the literature. © 2009 IEEE.