Obesity is considered the second most common health problem in pet cats in developed countries. This study used prospective data from a longitudinal study of pet cats (‘C.L.A.W.S.’, www.bristol.ac.uk/vetscience/claws) to identify early-life risk factors for feline overweight/obesity occurring at around two years of age. Data were collected via five owner-completed questionnaires (for cats aged two–six months, six months, 12 months, 18 months and two years respectively) completed between May 2011 and April 2015. Owner-reported body condition scores (BCS) of cats at age two years, assessed using images from the 9-point BCS system (Laflamme, 1997), were categorised into a dichotomous variable: overweight/obese (BCS 6–9) and not overweight (BCS 1–5) and used as the dependent variable. Of the 375 cats with owner-reported BCS, 25.3% were overweight or obese at two years of age. Multivariable logistic regression models were built using stepwise forward-selection. To account for potential hierarchical clustering due to multi-cat households two-level random intercept models were considered but clustering had no impact on the analysis. Models were compared using Wald tests. Six factors were significantly associated with overweight/obesity at two years of age: being overweight or obese at one year of age (OR = 10.6, 95%CI 4.4–25.3); owner belief that BCS 7 was the ideal weight (OR = 33.2, 95%CI 8.5–129.4), or that BCS represented overweight cats but they would not be concerned if their cat were classified in this category (OR = 2.7, 95%CI 1.2–6.2), at questionnaire five completion; vets advising owners that the cat should lose weight, or making no comment on their weight, between one and two years of age (OR = 12.1, 95%CI 3.2–44.9 and OR = 3.9, 95%CI 1.5–10.3 respectively); owners giving their cat treats when they “felt happy” with them at 18 months of age (OR = 2.7, 95%CI 1.0 − 7.3); feeding ≥250 g wet food daily between two and six months of age (OR = 2.7, 95%CI 1.2–5.9), and feeding dry food as the only or major part (> 50%) of the diet at two years of age (OR = 2.1, 95%CI 1.0–4.2). These findings have the potential to reduce the current high prevalence of a widespread problem by informing preventive advice, and as such improving the health and welfare of pet cats.