Subclinical hypothyroidism (SCH) is a prevalent condition marked by elevated thyroid-stimulating hormone (TSH) levels with normal free thyroxine (FT4) and free triiodothyronine (FT3) levels. Despite its frequency, diagnostic and management practices for SCH vary widely, leading to inconsistencies in patient care. This systematic review aims to assess and consolidate current diagnostic criteria and management practices for SCH, identify discrepancies among guidelines, and provide evidence-based recommendations for optimizing patient management. A thorough literature search was performed in PubMed, Embase, Cochrane Library, and Scopus for studies published from 1990 to 2024. Inclusion criteria covered peer-reviewed original research, clinical guidelines, and reviews focusing on SCH diagnosis and management. Quality assessment of the included studies was conducted using the Newcastle-Ottawa Scale for cohort studies and the Cochrane Risk of Bias Tool for randomized controlled trials. Key data points extracted included diagnostic thresholds, management protocols, and reported outcomes. The review revealed substantial variability in diagnostic criteria for SCH, with differences in TSH thresholds and the use of thyroid antibody testing. Management strategies also varied, with some guidelines advocating treatment based on elevated TSH alone, while others considered patient age, cardiovascular risk factors, and symptomatology. The review also highlighted ongoing debates regarding the benefits of treatment, especially in older adults and those with comorbid conditions. This review highlights the need for standardized diagnostic criteria and management protocols for SCH. The variability in current practices underscores the importance of developing unified, evidence-based guidelines to enhance patient outcomes. Future research should focus on the long-term effects of different management strategies and the impact of individualized treatment approaches on diverse patient groups.