Lei was born on 16 December 1969 in Xiantao, Hubei, China. In 1987, he graduated from Mianyang Middle School and began attending Wuhan University, where he completed all credits within two years and graduated with a BA in computer science. He also started his first company during his last year in college.
In 1998, he was named an honorary professor at Wuhan University, his alma mater, where there is also a scholarship in his name.
In 2000, Lei founded Joyo.com, an online bookstore, which he sold for USD$75 million to Amazon.com in 2004.
In 2003, he was named an honorary professor at the Zhengzhou Institute of Engineering.
On 6 April 2010, Lei Jun founded Xiaomi Inc, a Technology company that manufactures smartphones, mobile apps, and other consumer electronics. His cofounders include Lin Bin, vice President of the Google China Institute of Engineering; Dr Zhou Guangping, senior Director of the Motorola Beijing R&D center; Liu De, department head of industrial design at the University of Science and Technology Beijing; Li Wanqiang, general manager of Kingsoft Dictionary; Wong Kong-Kat, principal development manager; and Hong Feng, senior product manager for Google China.
In 2014, he was named Businessman Of The Year by Forbes Asia.
In 2017, Lei Jun has an estimated net worth of US$6.8 billion.