PurposeThis paper aims to empirically examine the presence of a balance sheet channel (BSC) of monetary transmission mechanism (MTM) using firm-level panel data of Pakistan. It also explores the role of financial sector development (FSD) and firm age (FAge) in formulating the effect of monetary policy (MP) on the investment decisions of firms.Design/methodology/approachThe authors applied the two-step system generalized method of moments (SYS-GMM) estimator proposed by Blundell and Bond (1998) to carry out the empirical analysis. The final sample of the study includes 450 nonfinancial firms listed at the Pakistan Stock Exchange (PXS) during the period 1988–2021. The empirical framework of the study is based on the new classical model of investment. Different measures of MP are used to obtain the robust empirical evidence. To take into account the different dimensions of FSD, the index developed by Svirydzenka (2016) is utilized. To examine the moderating role of FSD and FAge, the interacted model is estimated, which enables the authors to estimate the MP effects at different percentiles of the moderating variables.FindingsThe study’s findings confirm the existence of BSC by revealing that MP instruments have negative, significant effects on firms’ investment decisions. These findings suggest that during periods of tight MP, firms significantly cut their investment expenditures. The results of the interacted model show that both FSD and FAge play an important role in lessening the adverse effects of MP on firms’ investment policy. Specifically, the calculated total effects suggest that the negative effect of MP on investment is considerably weaker at the higher percentiles of FSD and FAge.Practical implicationsThe findings of the study have several important policy implications for different stakeholders. Specifically, the evidence suggests that the monetary authorities should keep in mind the adverse effects of MP while designing tight MP. The tight MP will have a negative effect on firm investment, which, in turn, will adversely affect firm growth and subsequently the growth rate and level of employment in the economy. Thus, during episodes of tight MP, the authorities should provide other facilities such as a friendly tax environment, better legal and regulatory framework, special credit arrangements, and provisions of loan guarantees. The findings of the moderating role suggest that the government may improve FSD to minify the adverse impacts of tight MP. Finally, the findings suggest that the government should design external financing-friendly policies to provide more opportunities to newly established firms to avoid tight MP’s effects.Social implicationsThe findings of the moderating role suggest that the government may improve FSD to minify the adverse impacts of tight MP. Finally, the findings suggest that the government should design external financing-friendly policies to provide more opportunities to newly established firms to avoid tight MP’s effects.Originality/valueThere are three significant contributions of the paper. Firstly, it provides empirical evidence on the existing of BSC of MTM using firm-level panel data spanning over 43 years for an emerging and small economy, namely Pakistan. Secondly, it examines the moderating role of FSD and FAge in formulating the effects of MP. Finally, it presents the total impact of MP at different percentiles of FSD and FAge, which definitely broadens the understanding of MTM through indirect channels.