Magnetic topological semimetals provide a fertile ground for exploring how long-range magnetic order can alter electronic band structures and generate novel quasiparticles such as Weyl fermions. Here, we investigate the coupled magnetic and electronic structure of single-crystalline EuAgAs, a hexagonal pnictide whose magnetic ground state has remained elusive. Using neutron diffraction and resonant elastic X-ray scattering, we identify an unusual magnetic ordering sequence with two successive phase transitions at TN1 = 12 K and TN2 = 8 K. We observe two slightly different magnetic propagation vectors, one associated with TN1 and the other with TN2. Spherical neutron polarimetry reveals that the magnetic structure is a transverse helix aligned along the c axis with a period that is approximately twice the c lattice parameter. First-principles calculations for the helical phase predict subtle band folding effects and the emergence of effective higher-order Weyl nodes. These topological features appear near the calculated Fermi energy E_F which, however, lies above the position of E_F obtained from angle-resolved photoemission spectroscopy so could not be probed in this study.