AT&T Galaxy S3 is one of those lucky devices that can now run the latest Android 6.0 Marshmallow without any problems. A team of developers have ported the CyanogenMod 13 for Galaxy S3 and today, they have uploaded the first version of the custom ROM. Currently, there are some minor issues in the ROM and like the rest of the ROMs these will be fixed with the coming update.

If you are an AT&T Galaxy S3 user and want to try out this ROM on your device then you need to follow our detailed guide. Before proceeding, we need to remind our readers that this ROM is a custom ROM and is not officially supported by Samsung. If you are ready then follow the steps below.


  • Before proceeding, make sure you have properly taken the backup of your important data including personal photos and videos.
  • Your device should have more than 60 percent battery to prevent any unexpected shutdowns during the process.
  • You have installed the  Samsung Galaxy S3 USB drivers on your PC.
  • Your device must be rooted and have Custom Recovery like CWM installed.
  • You should have enabled the USB debugging mode. If you not then go to settings > Developer Options and enable it.
  • This guide is only for Samsung Galaxy S3 I9300. Don’t try it on other variants.

How to Install Android 6.0 Marshmallow Custom ROM on AT&T Galaxy S3

Step No 1: First, you need to download the Android M Custom ROM and Gapps on your PC.

Step No.2: Copy the files and place it in the root directory of your SD Card.

Step No.3: Now, turn off your device and boot into recovery mode. Turn the device ON while pressing and holding Power + Home + Volume Up keys at the same time till the TWRP logo appears. Navigate to the recovery screen and select Backup.

Step No.4: After backup is finished. Perform Wipe of Data, Dalvik Cache and System.

Step No.5: When completed. Go back to the main menu of the recovery and select install. Now navigate to the root directory and select the ROM you have downloaded in the first step and tap swipe to Confirm Flash option

Step No.6: Once installation is compeleted, again perform a Wipe Dalvik cache.

Step No.7:Now, go the main screen of the recovery and select Reboot.

Step No.8; Apply the same above steps for installing the Gapps.

Step No.9: Now restart the device and it’s done.

That’s it. Your AT&T Galaxy S3 has been updated to Android 6.0 Marshmallow. If you have any questions let us know in the comments


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