<p>The present study intends to comprehensively investigate the thermal characteristics of poly(3-hydroxybutyrate) (PHB) when combined with commercial (polyethylene glycol, PEG) and natural, cardanol-derived plasticisers. The impact of plasticisers on isothermal and non-isothermal crystallisation kinetics and their ability to increase flexibility were investigated using differential scanning calorimetry (DSC). The Avrami approach cannot characterise isothermal crystallisation kinetics accurately as PHB exhibited an extensive range of secondary crystallisation, also confirmed by the crystallisation activation energy calculated by the Friedman method. Findings indicate that the addition of plasticisers significantly reduced the crystallisation rate in the nucleation-controlled temperature range. However, the Avrami exponent was observed to be temperature-dependent for plasticised PHB. A comparison analysis was conducted to compare the Ozawa and Mo-Liu models for non-isothermal crystallisation. The Mo-Liu model predicts a maximum degree of crystallinity independent of the cooling rate and demonstrates a strong agreement with experimental data. Conversely, the Ozawa model cannot accurately describe the non-isothermal crystallisation kinetics of PHB. The equilibrium melting temperatures were calculated using the nonlinear regression technique, applying the Hoffman-Weeks approach, which further correlated with the classical Flory–Huggins equation, revealing that the addition of plasticisers notably decreased the equilibrium melting temperatures of PHB.</p>