Graphene oxide (GO) emerged as a new carbon-based nanomaterial known for its complex carbon structure and strength properties. In the current investigation, an attempt is made to improve the workability of GO-concrete; fly ash is introduced to form a cost-effective mineral admixture. The effects of GO addition at 0.15% and replacement of fly ash at 10%, 20% and 30% on fluidity, mechanical and microstructure properties of highstrength concrete were investigated. The experimental results showed that fly ash plays a significant role to enhance fluidity and hence workability, owing to the ball effect, size gradation and less water requirement. Therefore, the influence of GO on the decrease in fluidity was counterbalanced by fly ash. Also, GO counterbalanced the fly ash influence on delaying early-age strength progress. The replacement of fly ash at 20% and GO addition at 0.15% showed an enhancement of compressive, split tensile and flexural strengths by 6%, 7% and 12% at 7 days and by 10%, 12% and 16% at 28 days, respectively, in comparison with control concrete. The microstructure studies of SEM, EDX, FTIR and XRD indicated that the formation of better hydration phases leads to the densification of microstructure in FA-GO-concrete. The present investigation shows an advantage of combining GO and fly ash which play a synergistic role and counterbalance the drawbacks of one another.