Husayn was the grandson of Amir Qazaghan, who had killed Qazan Khan and taken control of Transoxiana. After his grandfather's assassination he set out to recover that position, and in doing so allied with Timur, who married his sister and became his brother-in-law.
When Moghulistan invaded in the early 1360s the two fought side by side, and after their heavy defeat at the Battle of the Mire in 1365 they withdrew together south of the Amu Darya. But once the Moghul army had gone, the relationship deteriorated fast.
Husayn levied heavy taxes to build fortifications and keep his army, which chiefs and townspeople exhausted by war could not bear. As Timur won support by paying some of those levies on others' behalf, Husayn's following shrank, and in 1370 his own commanders in Balkh went over one after another until he was captured and killed.