This result sees Alex Neil's side move into 10th place, whilst Aitor Karanka's woeful home form continues, dropping down to 19th place and six points adrift of the relegation zone.
Story of the match
The game gradually petered out into a scrappy affair with limited chances until the 30th minute, when winger Iván Sánchez skipped past his defender before curling an effort goal wards which had to be tipped to safety by Preston goalkeeper, Daniel Iversen.
George Friend picked up a late booking for a poor challenge on Brad Potts as both defences were vigilant resulting in limited openings for each side.
The second half commenced and Preston nearly took the lead just minutes after the restart as Potts found space in the centre of the box, hitting the right post with a strike which had Neil Etheridge well beaten.
Preston asserted their dominance as the second half grew on, and the visitors took the lead on 61 minutes as Jayson Molumby teed up Scott Sinclair for his eighth goal of the season.
Birmingham nearly hit back minutes later, as substitute Jonathan Leko crossed into Jeremie Bela, whose header was saved well by the outstreched Iversen.
Substitute Lukas Jutkiewicz and Ivan Sunjic saw late efforts go wide as Preston secured a vital win which puts the Lilywhites seven points away from the top six. Birmingham sink to 19th as relegation worries continue to grow for Blues.
Takeaways from the match
Both teams will be disappointed with the first half, but Preston managed to find an opening which sees them leave Birmingham with all three points. Birmingham had more possession, more shots as well as more shots on target but Preston showed Championship experience in how to grind out a win. Preston will look to kick on against Reading on Sunday, but worrying times could be ahead for Birmingham, who face an important clash against relegation rivals Coventry City on Saturday.
Player of the match
Sinclair was the difference in this fixture, grabbing the goal which eased Preston worries in a hard-fought win. The winger has scored eight goals in Championship action this season, and will play a vital part if Preston look to make a play-off surge.