Ollie Banks scored the only goal of the game on four minutes as he curled an effort with the outside of his boot into the far corner.
Latics came under a lot of pressure in the game but managed to hold on and they recorded back-to-back wins for the first time this season and moved them further clear of the relegation places.
Manager John Sheridan made three changes to the side which beat Coventry City at the weekend.
Paul Green, Lee Erwin and Banks came into the starting 11 but it would be the visitors Charlton Athletic who had the first opportunity of the game.
The game was only 15 seconds old as Josh Magennis beat the offside trap but blazed his shot over the crossbar when one-on-one with Connor Ripley.
Latics responded well and took the lead on four minutes through Banks.
It was good football from Latics on the edge of the box, Chris Taylor laid the ball back to Banks and he struck with the outside of his boot into the top corner to give Athletic the lead.
Athletic continued to attack and were unfortunate not to extend their lead on 11 minutes.
Paul Green touched the ball through to Ryan McLaughlin on the right, he raced at the defence but unfortunately a heavy touch saw the goalkeeper collect the ball.
The visitors started to grow into the game with Magennis and Jonathan Botaka both going close midway through the half.
Magennis’ shot was blocked by Peter Clarke whilst Botaka’s cross was headed over the crossbar by Green.
Joe Aribo was the next to go close for the visitors but his effort went wide, whilst two minutes later, Ezri Konsa headed over Ripley’s crossbar.
On the half hour mark, Banks whipped a free kick over the crossbar before Lee Erwin’s strong run was brought to a halt in the penalty box.
Clarke almost doubled Latics’ lead on 36 minutes after Banks’ corner found the top goalscorer in the penalty box but his header rebounded off the post and was cleared.
Ripley was tested five minutes before the break as Konsa’s header forced the goalkeeper to push his dangerous effort wide.
From the resulting corner, Andrew Crofts glanced a header wide of the far post.
The visitors started the second half the stronger of the two sides and almost equalised two minutes into the half.
Jake Forster-Caskey’s corner found the head of Magennis but his effort flashed wide of Ripley’s near post.
All the pressure was coming from the visitors but Latics’ defence were handling the danger well as Charlton struggled to break through the stubborn defence.
On 55 minutes, Forster-Caskey forced goalkeeper Ripley to tip the ball over his crossbar following his fierce strike from 25 yards.
A brief stoppage in play followed as Aiden O’Neill received treatment on the field for an injury.
He was fine to continue and Latics started to turn the screw on the game.
Erwin managed to break free with the ball on the hour mark but he was halted in his tracks, whilst minutes later, Banks, who was impressive throughout, slid the ball through to the striker but he could not reach it before the goalkeeper.
Gerrard headed wide minutes later whilst whipped another free kick over the crossbar from the edge of the area.
Athletic were holding on well with the visitors forced to shoot from long range.
Substitute Lee Novak glanced a header goalwards late into the game but Ripley tipped his effort wide.
From the resulting corner, Ripley again was forced into action as he palmed Patrick Bauer’s effort over from 10 yards.
Novak took aim from 25 yards but again Ripley was behind the ball to save as the fourth official announced six minutes of additional time.
Athletic fans were doing their utmost to get behind the lads and substitute Michael Ngoo almost put the game to bed but struck over into additional time.
The referee finally blew time on proceedings as Latics recorded back-to-back wins for the first time this season.
Oldham Athletic: Ripley, Wilson, Clarke, Gerrard, Hunt, Green, Banks (Fane 89’), O’Neill, Taylor, McLaughlin, Erwin (Ngoo 78’).
Subs not used: Law, Flynn, Croft, Osei, Obadeyi.
Charlton Athletic: Rudd, Chicksen, Bauer, Crofts, Magennis, Mavididi (Novak 82’), Botaka (Holmes 58’), Konsa, Forster-Caskey (Watt 79’), Solly, Aribo.
Subs not used: Jackson, Phillips, Dasilva, Teixeira.
Goals: Oldham Athletic (Banks 4’) 1-0 Charlton Athletic
Attendance: 2,946 (204 visiting supporters)