An analysis of geomagnetic disturbances and global ionospheric electron density perturbations during the 2015 St. Patrick’s Day geomagnetic storm is presented in this paper. GPS observations from worldwide IGS stations are used and analysed through GPS-TEC analysis application developed by Gopi Seemala to get VTEC profiles. The St. Patrick’s geomagnetic storm covers the interval of 15-23 March 2015, when transient solar eruptions (a prolonged C9-class solar flare and associated CMEs on 15 March) and a strong geomagnetic storm during 16-18 March (Dst dropped to -223 nT) were reported. This geomagnetic storm led to complex effects on the ionosphere. The global maps have been created after analysing VTEC profiles at Low, Mid and High-latitudes over different longitudinal sectors. Major features of the positive and negative ionospheric storm development are observed in Asian, European and American Low, Mid and High-latitudes.