The study examined Sylhet city slum dwellers’ education, housing, occupation, sanitation, health services, diseases, lack of fundamental knowledge and training, and other issues to determine their livelihood situation. Data were collected through face-to-face interviews with 138 randomly selected respondents from nine wards (No. 6, 7, 9, 10, 11, 12, 19, 23, and 26) of Sylhet City from September’2018 to March’2019. Focus group discussion (FGD) was done to validate the information. Collected data were analyzed using descriptive statistics such as frequency counts, percentages, means, standard deviation, and ranks in SPSS. The majority of the slum residents (43.5%) came from the Sunamganj district in the research area. An estimated 53.62% of them were illiterate. According to the findings of this study, every family lives in a slum in a deplorable environment without sanitation. The slum dwellers work as day laborers (31.88%), rickshaw pullers (18.84%), masons (14.49%), home servants and drivers (8.70%), service holders and shopkeepers (4.35%), hawkers (2.90%), etc. Monthly slum income ranged from Tk. 7,500 to 14,950. About 59.42% of slum people depended on pharmacy/quack for their treatment. It was also observed that most of the slum dwellers were affected by various kinds of seasonal and waterborne diseases like fever (85.51%), cough (50.72), diarrhea (43.48%), skin diseases (29.71%), headache (20.29%), jaundice (14.49%), dental problem (13.04%), asthma and back pain (10.14%), diabetic (7.25%) etc. Possible reasons for diseases were reported as the damp environment (46.38%), lack of balanced nutrition (43.48%), water pollution (30.43%), adulterated food (26.09%), etc. They require different need-based training and support for their livelihood improvement. It was supposed that slum people lacked basic requirements, the bottleneck of a sustainable city. Thus, the findings recommend a holistic approach to address multidimensional sustainability challenges that influence slum residents’ lives within the country’s purpose-driven development policy for Sustainable Development Goals (SDGs).