Background <p>Gestational weight gain (GWG) is a significant indicator of the mother’s health and the quality of life of her growing fetus. However, little is documented on knowledge, attitudes, and practices regarding GWG management in low— and middle-income countries, particularly in Tanzania. This study aimed to examine knowledge, attitudes, and practices regarding gestational weight gain among pregnant women, their partners and female household members, and healthcare providers in Tanzania.</p> Methods <p>A cross-sectional mixed-method study was conducted between January and March 2024 at Mnazi Mmoja Hospital and Buguruni Health Center in Dar es Salaam, Tanzania. Quantitative data were collected on knowledge, attitudes, and practices regarding GWG through structured researcher administered questions to pregnant women (<i>n</i> = 100). Qualitative data were collected through 37 in-depth interviews with pregnant women and focus group discussions with partners (<i>n</i> = 24) and female household members (<i>n</i> = 18). Descriptive analysis was used to analyze quantitative data from structured questions, and thematic analysis to analyze qualitative data.</p> Results <p>GWG during pregnancy was confirmed as an essential indicator of maternal and fetal health. Most pregnant women (74%), partners (79.2%), female members (77.8%), and health care providers (100%) perceived GWG as very important for fetal health. However, excessive or inadequate weight gain was reported to be unfavorable, although few knew the recommended weight gain during pregnancy. Family members encouraged women to gain weight and eat as if they were “eating for two”. Weight measurements were routinely conducted; however, unless alarming signs were observed, results were not communicated to the women due to personnel shortages and heavy workloads. Healthcare providers lacked competence in GWG counseling. Only 58% of healthcare providers reported being aware of at least one GWG guideline. Inaccurate and unreliable weighing machines challenged the consistency of gestational weight management during antenatal care visits.</p> Conclusions <p>Limited knowledge of recommended gestational weight gain, limited counseling skills, and unreliable weight-management amenities challenged GWG management practices. Efforts to improve understanding and practices regarding GWG among stakeholders are critical for strengthening weight-gain measurement and management during pregnancy.</p>