We report the effect of hydrostatic pressure on the electronic state of the antiferromagnet UIrGe, which is isostructural and isoelectronic with the ferromagnetic superconductors UCoGe and URhGe. A series of electrical resistivity measurements in a piston - cylinder- type cell and a cubic-anvil cell were performed at hydrostatic pressures up to 15 GPa. The Neel temperature decreases with increasing pressure. We constructed a p-T phase diagram and estimated the critical pressure pc, where the antiferromagnetism vanishes, as similar to 12 GPa. The antiferromagnetic/paramagnetic transition appears to be first order. We suggest a scenario of competing antiferromagnetic inter-J- and ferromagnetic intra-J*-chain interactions in UIrGe. A moderate increase in the effective electron mass was detected in the vicinity of pc. A discussion of the electronic specific heat. and electron - electron correlation term A using the Kadowaki-Woods relation is given.