Peter-John Collins, a former tax partner at PricewaterhouseCoopers (PwC), has been deregistered by the Tax Practitioners Board and banned from the profession for two years.
Mr Collins had been briefed confidentially by Treasury on measures to improve tax laws.
These included rules to stop multinationals avoiding tax by shifting profits from Australia to tax and secrecy havens.
An investigation found Mr Collins leaked the confidential information to some PwC partners and staff.
The tax board also found PwC failed to manage conflicts of interest, breached its legal obligations and the professional code of conduct.
The firm has been ordered to improve processes and training to ensure conflicts of interest are managed better.
A PwC Australia spokesperson said the firm acknowledged it should have had procedures to prevent such a breach.
"In each case this failed the standards we set for PwC and we deeply regret this occurred," the spokesperson said.
"The firm has since reviewed and strengthened its controls, policies and training with respect to conflicts of interest."
Tax board chairman Ian Klug said the board would not tolerate tax practitioners who abused their positions of trust and failed to act with integrity.
"Some tax practitioners are involved in confidential law reform discussions to share their wisdom and experience and to support the public interest," he said.
"Leaking confidential information in these circumstances might be seen to elevate personal and commercial profit, breaching public interest, legal and ethical obligations.
"The board will not tolerate those practitioners who act without integrity."
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