Shareholder Political Transparency Act of 2021 This bill requires an issuer of securities to disclose information related to expenditures for political activities. Specifically, issuers must disclose quarterly any such expenditure, including by identifying any candidate the expenditure was made in relation to and any trade association or other tax-exempt organization that received dues or other payments that may be used for political activities. Annually, issuers must report on expenditures for political activities made in the previous year over $10,000 and information related to anticipated expenditures for the next year. The Government Accountability Office must report on the effectiveness of the Securities and Exchange Commission's oversight of these reporting and disclosure requirements.