BackgroundNumbers of GP locums in the NHS have grown in recent years, yet evidence on the scale and scope of the locum workforce in general practice is sparse.AimTo identify characteristics, geographical patterns, and drivers of GP locum use.Design and settingObservational study of routine data from general practices in England.MethodDescriptive analyses of national GP workforce data between December 2017 and September 2020 were conducted to determine the volume and geographical distribution of locum use and examine the characteristics of locums compared with other GP types. Locum full-time equivalent (FTE) was modelled using negative binomial regression and estimated incidence rate ratios (IRRs) for associations between outcome and characteristics of practices and population.ResultsIn December 2019, total locum FTE was 1217.9 compared with 33 996.6 for total GP FTE. Locums represented 3.3% of total GP FTE, which was fewer than other GP types. Median locum age was 42 years (interquartile range [IQR] 36 to 51) FTE and the majority were UK qualified (660 of 1034 [63.8%] total locum FTE), were male (642.6 of 1178.9 [54.5%] total locum FTE), and had long-term employment (834.1 of 1127.9 [74.0%]) total locum FTE. Rurality (IRR 1.250 [95% CI = 1.095 to 1.428]), inadequate Care Quality Commission ratings (IRR 2.108 [95% CI = 1.370 to 3.246), and single-handed practice (IRR 4.611 [95% CI = 4.101 to 5.184) were strong predictors of locum use. There was substantial variation in locum use between regions.ConclusionGP locum use remained stable over time. Compared with other GPs, locums were younger male GPs, a substantial percentage of whom did not qualify in the UK, and those who served underperforming practices in rural areas. This is likely to reflect recruitment or high turnover challenges in these practices/areas and can provide a greater understanding of general practice workforce challenges in England.