In the last decade, the Iranian economy has witnessed fundamental changes in its tax system, which have been carried out with the aim of transitioning from an oil economy to a tax-based economy, financial transparency, and economic justice. This research, with a comprehensive and analytical approach, examines the effects of two important legal events, namely the “Amendment to the Direct Taxes Law of 1394” and the “Implementation of the Value Added Tax Law,” on the value of companies listed on the Tehran Stock Exchange. The importance of this issue stems from the fact that taxes not only affect a company’s cash flows as a cost, but also change valuation parameters through the channels of capital structure, agency costs, and information risk. In this article, first, theoretical foundations including theories of capital structure (static balance and hierarchy), agency theory, and theories related to working capital in the context of value added tax are explained. Then, an analysis of key legal articles is presented, including Article 97 (eliminating the ad hoc method), Article 132 (investment incentives), and Article 105 (rate fixation). The literature review shows that the 2015 reforms, especially the elimination of the ad hoc method of recognition, have had a positive relationship with firm value by reducing information asymmetry and systematic risk arising from auditor bias. On the other hand, although the VAT has created short-term liquidity challenges for industries with long receivables collection periods, in the long run it has helped improve the quality of profits and firm value by making the supply chain more transparent and eliminating informal competitors. This study argues that the net effect of tax reforms on firm value is the result of the trade-off between “reducing the tax shield due to rate reductions” and “increasing value due to risk reduction and transparency,” which in recent years has tipped the scales in favor of transparency.