High-spin states in 126 I have been investigated by using in-beam γ -ray spectroscopy with the 124 Sn( 7 Li, 5n) 126 I reaction at a beam energy of 48 MeV. The level scheme of 126 I has been extended and modified considerably by adding about 80 new γ rays and establishing five new bands. The configurations have been tentatively assigned for the yrast, yrare, and other excited bands with the help of triaxial projected shell-model (TPSM) and cranked shell-model calculations. The first band crossing in the yrast band is found due to alignments of a pair of (h 11/2 ) 2 neutrons. The first and the second band crossings in the yrare band are caused by the alignments of a pair of (d 5/2 ) 2 protons and a pair of (h 11/2 ) 2 neutrons, respectively. Due to the successive excitations of two, four, and six quasiparticles, the alignments in the yrare band present a gigantic rising feature. The yrast band exhibits a signature inversion at low spins and becomes normal after a reversion spin of I rev = 14. The yrare band exhibits an abnormal signature inversion in which the signature inversion phase persists up to the highest spin. The signature inversions in 126 I are well reproduced and successfully interpreted by the TPSM calculations. Some features of chirality are found for the four-quasiparticle (4qp) part of the yrast band and the 4qp excited band 2.