Gartree opened in 1965 as a category C training prison but quickly changed its role and came within the high security system, reverting to a category B prison in 1992. Since then the population of indeterminate sentenced prisoners has been growing and in 1997 its role changed to that of a main lifer centre and is the largest lifer centre in the UK. HMP Gartree is run by HMPS, and is part of the East Midlands group of prisons. The prison #1 governor is Babafemi Dada who has been in charge since November 2019.
- A, B, C and D wings-Generic residential wings that are part of the original 1960s build and have since been refurbished. A- C wings have single cells only, and D wing also has two double cells.
- G wing induction/reverse cohort unit, opened in 2005-06. It has two double cells; the remainder are single cells.
- H wing Opened in 2005-06, it houses prisoners aged over 50 and the psychologically informed planned environment (PIPE) unit.
- I wing Houses 28 prisoners in 13 double and two single cells.
- Gartree therapeutic community (GTC) Holds up to 25 prisoners in single cells. Therapeutic community plus (TC+)For prisoners with learning difficulties or low IQ who require additional assistance and guidance, with 12 single cells.
- The segregation unit12 beds.
All the prisoners are in single cells after spending their induction period in double cells, and the capacity of the prison is 719.