The 46-year-old, the first local coach in six years to take charge of the Leone Stars, was unveiled in Freetown on Thursday.
Keister will also continue in his current job as coach of local premier league club FC Johansen, owned by Sierra Leone FA president, Isha Johansen.
His main task is to qualify the Leone Stars for the 2019 Africa Cup of Nations in Cameroon.
Keister has served as Leone Stars assistant coach to three foreign managers - Ghanaian Sellas Tetteh, Swede Lars Olof Matsson and Northern Irishman Johnny Mckinstry.
"Working under three foreign coaches has given me the experience and knowledge to be in this position," Keister told the BBC on Thursday.
"My appointment is a dream come true. We have a massive task to qualify for the Afcon finals."
Johansen congratulated Keister but warned him that the aspirations of seven million Sierra Leoneans lie on his shoulders.
Keister had previously served as head coach of the Leone Stars home based team as well as the Sierra Leone under-17 and under-23 national teams.
The former Leone Stars midfielder was born in Manchester and played for several lower league clubs in England, including Walsall, Chester City, Shrewsbury Town and Stevenage Borough.
He was capped 16 times by Sierra Leone between 1997 and 2003.
Former Sierra Leone international John Keister is the new head coach of the national team.