Born in Khashuri, Georgia, Ioseliani majored in Oriental studies at Leningrad University but did not graduate. He staged a bank robbery in Leningrad in 1948, for which he served 17 years in a Soviet jail. Released in 1965, he later served another sentence for manslaughter. He eventually returned to his native Georgia and graduated from the Georgian Institute of Theater Arts, where he became a professor.
Ioseliani rose to prominence as the leader of the Mkhedrioni, a heavily-armed paramilitary group which he founded in 1989. He attempted to take control of large areas of Abkhazia and South Ossetia with the goal of defeating regional separatist elements. In February 1991, his organisation was outlawed by President Zviad Gamsakhurdia and he was imprisoned along with other Mkhedrioni members.
In December 1991, Ioseliani escaped from prison and joined forces with rebel members of the Georgian National Guard to launch a violent coup d'etat that forced President Zviad Gamsakhurdia out of office in January 1992. He was one of the three leaders of the "Military Council" that ruled Georgia from January-March 1992. He subsequently became a powerful figure in the government of President Eduard Shevardnadze, who was forced to rely heavily on Mkhedrioni militiamen because of the weakness of the state security forces. Ioseliani made it clear who he thought was the senior partner: his office in the Georgian Parliament building was located directly above Shevardnadze's and he was constantly surrounded with armed followers wherever he went.
Ioseliani played a major role in the disastrous attempt to enforce Georgian rule in the separatist province of Abkhazia, which ended in a crushing defeat for government and Mkhedrioni forces in August-September 1993. Despite this, he was given a formal government position in September 1993 to enforce a national state of emergency. This gave him almost unlimited powers to detain people. He used these powers enthusiastically, imposing a severely repressive regime that was widely criticised by international human rights organisations. Supporters of the ousted Gamsakhurdia were vigorously targeted, especially in the pro-Gamsakhurdia region of Samegrelo in western Georgia, where the Mkhedrioni were accused of carrying out a number of extrajudicial killings. There were also widespread allegations that Ioseliani and his supporters were systematically "taxing" businesses and individuals in areas under their control.
On August 29, 1995, Shevardnadze narrowly escaped assassination in a bomb attack. The attack was blamed on a shadowy coalition of "mafia forces" including Ioseliani and others. He was detained in November 1998 and held for three years pending trial, then sentenced to 11 years for banditry, terrorism, and conspiring to kill Shevardnadze. He denied the charges and was eventually released in the spring of 2000 in a general amnesty of convicts. He suffered a heart attack on February 26, 2003 and died in a Tblisi hospital a week later.