Most newly arising mutations are deleterious for organismal fitness, yet can readily propagate within populations under a broad range of conditions. Evolutionary genetic processes able to counteract deleterious mutation accumulation include: a) generally beneficial mutations that improve organismal fitness irrespective of genetic background, b) compensatory mutations that specifically mitigate the effects of previously-acquired deleterious mutations through epistasis, and c) reversion mutations back to wildtype. The potential for spontaneous mutations to mitigate the effects of deleterious mutations alters our expectations for the population-level impact of deleterious mutation. However, the capacity of spontaneous mutations to restore ancestral phenotype and the molecular genetic patterns of compensation are still poorly understood in eukaryotic systems. We performed a mutation accumulation (MA) experiment—where mutations are allowed to accumulate in replicate lineages evolving in population sizes of one (i.e., extreme genetic drift)—using a mitochondrial-deficient mutant strain of Caenorhabditis elegans nematode, gas-1. This strain has lower levels of fitness compared to wildtype. Mutation accumulation is expected to result in further fitness decline due to accumulated deleterious mutations. However, the lines experienced partial phenotypic recovery back to wildtype levels. Next-generation sequencing and bioinformatic analyses revealed several candidate single nucleotide polymorphisms (SNPs) responsible for this recovery. The purpose of this study was to determine the capacity of SNPs to restore fitness in gas-1. We introgressed the SNPs onto wildtype and gas-1 backgrounds, then performed life-history assays to compare the introgressed strains with wildtype and gas-1 strains. We discovered that the introgressed strains experience a shift to earlier reproduction compared to wildtype and gas-1 strains and conclude that the SNPs are generally beneficial for fitness. This finding indicates that beneficial mutations are able to accumulate under extremely unfavorable population genetic conditions.