Magnetism in EuNiIn4 is studied using specific heat, magnetic susceptibility, magnetization, Eu-151 Mossbauer spectroscopy, and neutron diffraction experiments. The specific heat exhibited two magnetic transitions at T-N1 = 15.2 K and T-N2 = 14.3 K at zero magnetic field. An antiferromagnetic ground state of EuNiIn4 was observed to have a uniaxial magnetic anisotropy along the b axis using magnetic susceptibility and Eu-151 Mossbauer spectroscopy. Further, single crystal neutron diffraction experiments illustrated that this antiferromagnetic structure in the ground state is characterized by the commensurate propagation vector q = (1/2; 1/2; 1/2), which reveals no distinct anomaly at T-N2. The magnetization curve along the b axis at 2K was observed to exhibit four successive magnetic field-induced transitions up to 50 kOe, following which it increased linearly, resulting in saturated magnetization of 7 mu(B)/f.u. above 195.2 kOe, as expected of Eu2+ free ions. The magnetic phase diagram for H parallel to b in EuNiIn4 was found to have unique characteristics with five magnetic states in low magnetic fields.