For over a century, the Hall effect, a transverse effect under an out-of-plane magnetic field or magnetization, has been a cornerstone for magnetotransport studies and applications. Modern theoretical formulation based on the Berry curvature has revealed the potential that even an in-plane magnetic field can induce an anomalous Hall effect, but its experimental demonstration has remained difficult due to its potentially small magnitude and strict symmetry requirements. Here, we report observation of the in-plane anomalous Hall effect by measuring low-carrier density films of magnetic Weyl semimetal EuCd_{2}Sb_{2}. Anomalous Hall resistance exhibits distinct threefold rotational symmetry for changes in the in-plane field component, and this can be understood in terms of out-of-plane Weyl points splitting or orbital magnetization induced by the in-plane field, as also confirmed by model calculation. Our findings demonstrate the importance of the in-plane field to control the Hall effect, accelerating materials development and further exploration of various in-plane field-induced phenomena.