Abstract <p>Ni-based superalloys, used in turbomachinery components, are exposed to high temperatures during service, but also experience cyclic loads at room temperature (RT). High temperature exposure induces microstructural changes that influence their RT fatigue behaviour. To address this, fatigue crack growth (FCG) behaviour of the polycrystalline Ni-based superalloy, Haynes 282, in the solution-treated and aged condition (750&#xa0;°C for 6000 hours) at load ratios (<i>R</i>) of 0.1 and 0.5 is studied at RT. Ageing facilitates the growth of <i>γ</i>′ precipitates, M₂₃C₆, MC, M₆C, and Topologically Close Packed (TCP)-<i>µ</i> phases, but marginally affects the grain size and distribution. The fatigue threshold, Δ<i>K</i>_Th, of the aged sample is marginally higher than that of solution-treated sample and exhibits sensitivity to <i>R</i>. Alternately, stage II steady-state crack growth rates are insensitive to <i>R</i>, but the aged sample exhibits 1.7 and 1.8 times lower FCG rates than the solution-treated sample at <i>R</i> ~ 0.1 and 0.5, respectively. Both samples show similar Paris slopes (<i>m</i> ~ 3.6 to 3.8), indicating similar fatigue mechanisms in the steady-state regime. Post FCG test, TEM investigations near the crack surface reveal dense network of dislocations, stacking faults, and deformation twins. Differences in steady-state FCG rates are explained using Rice’s damage accumulation model, correlating the crack growth rates to yield strength and ductility. Maximum stress estimates ahead of the crack tip are compared with flow and critical twinning stress to rationalize twin formation. Finally, the sensitivity of FCG rates to <i>R</i> in the near-threshold and steady-state regimes is discussed and future perspectives are provided.</p> Graphical Abstract <p></p>