<p>Multifunctional smart coatings synthesised using green organic materials derived from waste floral biomass is a potential and sustainable material resources which is being underutilised and can be value added to generate chemicals and materials with properties of anticorrosive, antimicrobial and self-healing. The present study focuses on the valorisation of marigold (<i>Tagetes erecta</i>) floral waste extract and the isolated phytochemical quercetagetin for exploring its use in development of nanocomposites and coatings with multifunctional characteristics like antimicrobial, anticorrosive, and self-healing. Comparative evaluation demonstrated superior corrosion inhibition efficiency for the hydroethanolic extract, leading to the isolation of the potent green corrosion inhibitor Quercetagetin (QCTGN). Formulation of smart nanocomposite coatings with varying extract and compound compositions revealed that the 3% QCTGN- mesoporous silica nanoparticles (MSNP) provided optimal corrosion prevention for mild steel in 3.5 wt.% NaCl solution. Nyquist plot analysis illustrated a significant increase in charge transfer resistance, signifying excellent corrosion protection for mild steel. Potentiodynamic polarization studies indicated a notable decrease in E_corr and i_corr values, with an inhibition efficiency of 99.95% compared to bare alloy for mild steel. The coating exhibited potent antimicrobial properties against both gram-positive and gram-negative bacteria, with complete self-healing of the surface defect within 48&#xa0;h.</p> Graphical Abstract <p></p>