Synthesis of fine chemicals from the chemical fixation of CO₂ is one of the attractive research areas of today to utilise greenhouse gas CO₂ in a greener pathway. A flower-like silver nanoparticle grafted mesoporous magnesium oxide (AgNPs@m-MgO) nanocomposite has been prepared by a facile in situ pathway. The materials are characterised by XRD, FTIR, UV-vis, TG-DTA, FESEM, HR-TEM and N₂ adsorption–desorption studies. This AgNPs@m-MgO material showed a mesoporous nature with good surface area. It indicated brilliant catalytic activity for both the carboxylation of terminal alkynes by chemical fixation of CO₂ (1 atm) and the acylation of various amines by utilizing acetic acid as a reagent in solvent-free conditions showing yields up to 98% and 99% of the propiolic acid and acetamide products, respectively. The reusability of this catalyst has also been verified and it showed high recycling efficiency for both the reactions together with no considerable catalyst deactivation.