Global energy demand and depletion of fossil-derived fuels have posed an alarming need for alternate fuels. Lignocellulosic biomass is one of the most promising sustainable carbon-rich feedstocks that can be directly converted to biofuels via fast pyrolysis technique. It involves thermochemical decomposition at very high heating rate (~104 °C s-1), moderate temperatures (400-600 °C) and short residence time (1-5 s) in inert ambience to yield bio-oil. However, significant presence of oxygen-containing chemicals in bio-oil is the root cause of various unenviable properties. The prime objective is to minimize the substantial amount of oxygen content in bio-oil by selectively altering the organic oxygenates into hydrocarbons through deoxygenation pathways. Accordingly, catalytic upgrading of pyrolysis vapours in hydrogen ambience is a promising strategy to tailor the chemical composition of bio-oil to a greater extent via hydrodeoxygenation (HDO). However, it is mandatory to understand the ex-situ upgradation kinetics of organic vapours on the catalyst surface. To this end, mechanistic insight into deoxygenation of catalytically upgraded representative biomass pyrolysates such as guaiacol and furfural over protonated Zeolite Y catalysts of different Si/Al ratios were investigated in this study. Analytical pyroprobe connected with Gas Chromatograph/Mass Spectrometer (Py-GC/MS) served in testing the HDO activity of catalysts. The use of catalysts significantly led to better HDO producing remarkable aromatic hydrocarbons in the condensed phase. Protonated Zeolite Y (Si/Al ratio: 5.1:1 and 30:1) catalysts converted guaiacol into valuable chemicals, viz. benzene, toluene, and xylene (BTX) in major quantities. Notably, 100% conversion of guaiacol and furfural were achieved with Zeolite Y (5.1:1).