Low-quality palm oil (LPO) with high free fatty acid (FFA) content (9.66%) can be pretreated for biodiesel production through acid-catalysed esterification. However, homogeneous acid catalysts exhibit challenges in recyclability and separation despite their high catalytic efficiency. Magnetic composites (Fe₃O₄/PVA) as support materials for acid catalysts are a viable protocol for improving recyclability and separation performances. In this study, sulphonic acids and their deep eutectic solvent (DES) counterparts (formed with paracetamol at a 3:1 molar ratio) were supported on Fe₃O₄/PVA to yield heterogeneous solid acid catalysts for FFA esterification in LPO. From the screening results, Fe₃O₄/PVA/PTSA was determined as the best performing catalyst. The optimised reaction conditions were determined: 10 wt.% catalyst loading, 20:1 methanol-to-oil molar ratio, 5 hr of contact time and at 60°C, resulting in an FFA conversion of 79.81%. Fe₃O₄/PVA/PTSA exhibited fair recyclability performances and stability with > 65% FFA conversion after five successive runs. FFA esterification reaction using Fe₃O₄/PVA/PTSA was determined to require an activation energy of 43.72 kJ/mol following a simplified pseudo first order rate of reaction. Pristine sulphonic acids exhibited higher compatibility to be supported on Fe₃O₄/PVA magnetic composite than their DES counterpart, with Fe₃O₄/PVA/PTSA being a viable catalyst for the pretreatment of low-quality oils through FFA esterification.