He was born in Tehran, Persia as Mehdi Nuri. Mirza Mehdi was his mother's favourite child. Mihdí did not remember his once luxurious life as at the age of four his father was arrested and imprisoned on account of his faith. The family were left in penury and his sister later recollected how the siblings would hold each other and weep. When his family were exiled to Baghdad, the family thought it necessary to leave Mírzá Mihdí in Persia as a result of his health. He was left to the care of his maternal great-grandmother and his paternal aunt. The separation was hard for his family, especially his mother. At the age of twelve, he rejoined his family in Baghdad. There he accompanied his father through all his exiles and grew very close to him. He later became the amanuenses of Baháʼu'lláh and a staunch companion. He was beloved by the Baháʼís; revered in a similar sense to ʻAbdu'l-Bahá and was noted for his meekness, piety, purity and sincerity. Whilst rapt in prayer, chanting the Ode of the Dove and pacing on the rooftop, Mírzá Mihdí fell through a skylight, and the wooden crate that he fell onto pierced his ribs and injured his lungs. Baháʼu'lláh was horrified and asked for a physician to attend his son. However, by this time it was too late. His mother was especially hurt and poignantly caressed her blood-soaked son shortly before his death. Baháʼu'lláh was heard lamenting “Mihdí! O Mihdí!” as his son was dying. His companions surrounding him on his death-bed remember his courtesy despite his pain, and even apologizing that he was lying before their presence. He died on June 23, 1870, at the age of twenty-two. His dying wish was that the believers would attain the presence of Baháʼu'lláh, a wish which the broken-hearted Baháʼu'lláh accepted. His body was taken away and buried in a Muslim cemetery. His sister collected the blood-soaked clothes of Mihdí and other relics. These are seen in the International Archives in Israel. Baháʼu'lláh eulogized his son and connected the subsequent easing of restrictions and pilgrims' ability to visit him to his dying prayer. He wrote that his death caused “the Concourse on high to lament”. He also exalted his death, comparing it to the intended sacrifice of Abraham's son, the crucifixion of Christ and the martyrdom of the Imam Husayn. Baháʼu'lláh also named him the Purest Branch. The exiles and companions commented that he had been a "pillar of strength" amongst the exiles and adored for his gentleness and patience. Shoghi Effendi later removed the body of Mírzá Mihdí and reinterred it alongside his mother in the gardens below the Arc on Mount Carmel, Haifa, in an area now called the Monument Gardens.
