[1] He strongly advocates human rights for all regardless of religious ideology or belief and has created in calligraphy from the Torah, Psalms and Quran to foster unity amongst religions.

He was first arrested in August 1989 by order of the Special Clerical Court for privately criticizing and opposing the selection of Ayatollah Khamenei as Supreme Leader.

After spending two months in solitary confinement in Ward 240 of Evin Prison, he was sentenced to five years in prison, 40 lashes, and a ban on delivering of Islamic seminary subjects and public speaking on charges of insulting the Supreme Leader and government officials, inciting public opinion against the regime, spreading rumors, and disseminating false information.

In 1995, the Ministry of Intelligence arrested Mr. Masoumi-Tehrani and Ayatollah Ale-Es’haq for publishing statements from the "Party of Freedom-seeking Clerics of Iran," which had a notable impact among the clergy.

After spending four months in solitary confinement at Towhid Detention Center (formerly the Shah's Joint Anti-Sabotage Committee), they were sentenced to one and a half years in prison and received 80 lashes (40 each) on charges of insulting the Supreme Leader, conspiracy against national security, violating prior rulings, and producing and distributing misleading statements.

Thus, in April 2001, Mr. Masoumi-Tehrani decided to provide a calligraphed and illuminated version of the Book of Psalms of Prophet David and present it to the US authorities[10] In 2002, Mr. Masoumi-Tehrani issued a statement condemning the first suicide bombing in Israel, which had a significant impact among scholars and religious figures, encouraging them to criticize the Islamic Republic's policies towards Israel more openly[11] In 2004, the Book of Psalms was completed and dedicated, on behalf of the Iranian people, to the victims and the surviving families of the 9/11 in a public statement[12] In 2005, Mr. Mehdi Bahman personally delivered the Book of Psalms, accompanied by a letter, to the U.S. Embassy in Ankara.

In 2008, to protest the Islamic Republic's policies towards Israel and to highlight Iran’s historical connection with the Jewish people, Mr. Masoumi-Tehrani decided to calligraph and illuminate the Book of Ezra .

Despite repeated summons and complaints from the Ministry of Intelligence, which caused delays in the process, Mr. Masoumi-Tehrani completed the Book of Ezra in 2011 and released a statement.

He was invited by Dr. Mohammad Maleki, Nasrin Sotoudeh, and Narges Mohammadi to join the Campaign for the Gradual Abolition of the Death Penalty (LEGAM).

In 2016, Mr. Masoumi-Tehrani created an artwork consisting of eight symbolic pieces, aiming to promote solidarity and unity among the diverse religious communities in Iran.

Each piece of this artwork was dedicated to a specific religious group in Iran, including the Mandaeans in Ahvaz, Yarsanis in Kermanshah, Sunnis in Kurdistan, Zoroastrians in Yazd, and Iranian Jews in Tehran.

The piece intended for the Shia Muslim community remained in Mr. Masoumi-Tehrani's possession, awaiting presentation to an independent religious leader.

[22] Since submitting the Book of Ezra , Mr. Masoumi-Tehrani’s activities have mostly involved writing articles and giving interviews on religious, political, and social issues.

[23] In October 2022, during the height of the protests known as the "Mahsa Uprising," Mr. Masoumi-Tehrani was arrested by the Ministry of Intelligence and sentenced to five years of suspended imprisonment.