A Montgomery County jury on Thursday sentenced 43-year-old Brian Keith Balentine, whose criminal history was presented during the penalty phase.
Prosecutors say the robbery conviction involved a March 2008 theft in which an officer was slightly injured trying to stop Balentine.
Days earlier, Balentine had completed a 30-day jail term in Harris County for theft, one of three theft cases he faced since his 2006 parole.
But Balentine was also convicted of the 1984 slaying of Leroy Larson. The victim was fatally shot after stopping to help Balentine, who appeared to be having car trouble in Freestone County.
Defense attorney Earl Pryor said he was shocked at the life prison sentence.