Charlton Athletic 0 Preston North End 1 - Match report as the Lilywhites go top of the Championship with victory at The Valley
It was the first time since late 2006 that North End had occupied such a lofty position, the three points collected the day after the club had warned off Stoke City in their pursuit of Alex Neil.
Gallagher, on as a substitute for the injured Daniel Johnson, settled the contest from the spot in the 58th minute.
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Hide AdJayden Stockley got a shove from Addicks skipper Jason Pearce as he moved to meet a cross and Gallagher did the business from the sport.
The Lilywhites should have been ahead by the interval, with Tom Barkhuizen and Sean Maguire having good chances.
After eventually taking the lead, they held on to it and saw the game out in a fairly controlled way, although had five players booked in all during the afternoon.
Victory delighted the 1,128 travelling Preston fans who made the noon kick-off in South London despite there being no trains running in time for the start.
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Hide Ad"We're top of the league' they sang at the top of their voices as they filed out of the away end after full-time.
The North End starting XI had shown two changes from last week's win over Blackburn, with Stockley and Ben Davies coming into the side.
Stockley had impressed as a substitute against Rovers, while Davies was back after recovering from a twisted ankle.
They were in their usual 4-2-3-1 formation, Browne playing as the advanced midfielder with Johnson a little further back and Ben Pearson holding.
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Hide AdStockley led the attack, Barkhuizen on the right and Maguire down the left.
PNE had the contest's first sight of goal, Darnell Fisher on free-kick duties after nearly scoring with a late effort against Blackburn.
The right-back's effort was 25 yards brought a diving save low down from goalkeeper Dillon Phillips although he wasn't really troubled by it.
At the other end, Darren Pratley's shot deflected off Davies and went behind for a corner, while Declan Rudd parried a shot from Ben Purrington who had got room on the left hand side of the box.
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Hide AdSoon his chance, a Purrington cross found Conor Gallagher in the box but his flicked header went across goal and wide of the far post.
From the 20-minute mark onwards, North End had the better of the first-half play.
Pearson tried his luck with a shot from 25 yards which travelled well over the bar, an ambitious effort for a player with his goalscoring record.
North End were so close to opening the scoring in the 20th minute, a corner cleared out of the Charlton box but picked up Fisher covering any breakaway.
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Hide AdFisher took the ball down the left channel and sent over a low cross which evaded the home central defenders and found its way to Barkhuizen coming in on the far side.
But his low show was superbly blocked by Phillips at the base of the post and went behind for a corner.
The visitors lost the services of Johnson in the 31st minute after a foul by Naby Sarr left him struggling with a knock to his right foot.
Gallagher was summoned from the bench to replace him, slotting into Johnson's midfield role.
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Hide AdTwo good chances fell Preston's way in the closing stages of the first period.
With 39 minutes gone, Maguire cut inside from the left-wing into the box but instead of cutting the ball back for supporting team-mates, poked a shot goalwards which Phillips saved easily.
Then in the 44th minute Pearson's cross from the right-wing found Barkhuizen six yards out but he sent a header over the bar with just the keeper to beat.
Nine minutes into the second half, Gallagher played a short corner routine with Maguire, the substitute taking the return ball and hitting a low shot which a defender blocked at the expense of another corner.
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Hide AdPNE broke the deadlock from the penalty spot in the 58th minute, referee David Webb pointing to the spot after adjudging Stockley had been pushed by Jason Pearce as he moved to meet a cross into the box.
With Johnson off the pitch, it was Gallagher who stepped up and hammered the penalty past Phillips in front of the travelling 1,128 Preston supporters at that end of the ground.
A high lunge from Beram Kayal on Joe Rafferty in the Preston box earned the Charlton man a yellow card when it could quite easily have been red.
In the aftermath a word out of turn from Pearson earned him a booking, that his fifth of the season which rules him out of next Saturday's clash with Huddersfield through a one-match ban.
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Hide AdThe second half got niggly as it progressed, Davies having to be bandaged up after getting a cut on the head.
Fisher, Stockley and Barkhuixen were yellow carded in quick succession for fouls as they broke up the flow of play, much to the home side's anger.
Barkhuizen's yellow was for a trip on Conor Gallagher just outside the box, Josh Cullen lifting the free-kick to the far post where substitute Chuks Aneke couldn't get a touch and the ball went out.
In the 85th minute, North End won a free-kick of their own down the right channel, Gallagher whipping it into the box where it was met Stockley who headed inches over.
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Hide AdIn the second of seven minutes of stoppage-time, Barkhuizen got clear one-on-one as PNE broke on the counter.
He came into the box at an angle and keeper Phillips got a hand to his shot and managed to block when Maguire was better placed for a pass in the middle.
Charlton: Phillips, Lockyer, Pearce, Sarr (Leko 46) Solly, Pratley (Aneke 74), C Gallagher, Purrington, Kayal (Oztumer 89), Cullen, Bonne. Subs (not used): Oshhilaja, Lapslie, Davison, Maynard-Brewer.
PNE: Rudd, Fisher, Bauer, Davies, Rafferty, Pearson, Johnson (Gallagher 31), Barkhuizen, Browne, Maguire, Stockley. Subs (not used): Bayliss, Storey, Hughes, Ledson, Bodin, Ripley.
Referee: David Webb (Wearside)
Attendance: 16,027 (1,128 PNE)