Important issues for cognitive control are response selection processes, known to depend on fronto-striatal networks with recent evidence suggesting that striatal gamma-amino butyric acid (GABA) levels play an important role. Regional GABA concentrations have also been shown to modulate intrinsic connectivity, e.g. of the default mode network. However, the interrelation between striatal GABA levels, basal ganglia network (BGN) connectivity, and performance in cognitive control is elusive. In the current study, we measure striatal GABA levels using magnetic resonance spectroscopy (MRS) and resting state parameters using functional magnetic resonance imaging (fMRI). Resting state parameters include activity within the BGN, as determined by the low frequency power (LFP) within the network, and the functional connectivity between the BGN and somatomotor network (SMN). Specifically, we examine the interrelation between GABA, resting state parameters, and performance (i.e., accuracy) in conflict monitoring using a Simon task. Response control was affected by striatal GABA+ levels and activity within the BGN, especially when response selection was complicated by altered stimulus-response mappings. The data suggest that there are two mechanisms supporting response selection accuracy. One is related to resting state activity within the BGN and modulated by striatal GABA+ levels. The other is related to decreased cortico-striatal network connectivity, unrelated to the GABAergic system. The inclusion of all three factors (i.e., striatal GABA+ levels, activity within the BGN, and BGN-SMN network connectivity) explained a considerable amount of variance in task accuracy. Striatal neurobiochemical (GABA+) and parameters of the resting state BGN represent important modulators of response control. Hum Brain Mapp 36:4383-4393, 2015.