Install Android 6.0 Marshmallow On At&t Galaxy S3 [CyanogenMod 13]

Good news for At&t Galaxy S3. A new life has been given to this device. Android 6.0 Marshmallow based on unofficial CyanogenMod 13 custom ROM is now available for our beloved At&t Galaxy S3.This ROM has been compiled by XDA senior member matrixzone, so all the credit goes to him. If you’re interested in updating your At&t Galaxy S3 to Android 6.0 Marshmallow using a custom ROM, you may follow this guide as we will be helping you to do so.

In case you don’t know about the Android 6.0 Marshmallow, let’s have a recap on it. Android 6.0 Marshmallow is the 6th iteration in Android family. This firmware is the successor of Android Lollipop.  Android 6.0 Marshmallow, Googled worked on the cosmetics of the OS but in Android 6.0 Marshmallow, Google worked on the core Android system. There’s a number of powerful enhancements that make the Android 6.0 Marshmallow a major Android update. Google has upgraded the security of OS. New app permissions feature is pretty cool, and the doze mode for saving battery life is proved to be pretty awesome as well. Android 6.0 Marshmallow is available  for Nexus device or only a few top-notch devices at the moment.At&t S3

It’s quite a surprise for a device like Galaxy S3 to get a custom ROM based on unofficial CM 13.0 Android 6.0 Marshmallow because Samsung forgot this device after updating it to Android 4.3 Jelly Bean. By installing this custom ROM, you will be able to have a touch and feel of Android 6.0 Marshmallow on your phone. The ROM is still in development stages, so a number of crashes is expected. This ROM isn’t a daily driver, as of now it’s experimental. You may only install it if you’re interested in checking out a feel of Android 6.0. We do not recommend newbies to flash this ROM. Proceed with the flashing process if you have an idea about custom ROMs and you can handle any mishap(if occurs).



  • This guide is intended for At&t Galaxy S3 SGH I747 only. Do not try flashing this ROM on any other device.
  • Charge your phone up to 80% to make sure that your phone doesn’t die during the flashing process.
  • Flash latest TWRP recovery on your At&t Galaxy S3.
  • Make sure that you backup your important media content, ContactsCall Logs Messages. This is highly recommended just in case something goes wrong and you need to reset your phone.
  • If you already have rooted your device, use Titanium Backup to back up all your important apps + system data.
  • Also if you are using a custom recovery, it is recommended that you backup your current system using that first. [Just for the sake of safety]. Here’s our full Nandroid Backup guide.
  • You will have to go through Data Wipes during installation of this ROM, so make sure that you have backed up all the mentioned data.
  • Make an EFS backup of your phone before you flash this ROM.
  • You need enough confidence to flash this ROM.
  • Alright! Go ahead and flash the custom firmware, follow this guide to the letter.
  • Disclaimer: The methods involved in flashing custom roms and rooting your phone are highly custom and may result in bricking your device, and has nothing to do with Google or the device manufacturer that is SAMSUNG in our case. Also rooting your device will void its warranty and you will be no longer eligible for any kind of free device services by the manufacturers/warranty providers. In case of any mishap we may not be held responsible. Follow these instructions to the letter to avoid any mishap or bricking. Make sure that whatever you do, you are doing it at your own responsibility.


Install Android 6.0 Marshmallow On At&t Galaxy S3 [CyanogenMod 13]

  1. Download file.
  2. Download file for CM 13.
  3. Connect your phone to your PC now.
  4. Copy the both the .zip files to the storage of your phone.
  5. Now disconnect your phone and turn it off complete.
  6. Boot into TWRP recovery now, in order to do so, turn it on by pressing and holding Volume Up + Home Button + Power Key. You should see the recovery mode in a while.
  7. Now in TWRP  recovery, wipe cache, factory data reset and advanced options > dalvik cache.
  8. After wiping all these three, select “Install” option.
  9. Now select “Install > Choose Zip from SD card > Select cm-13…… file > Yes”.
  10. This will flash the ROM in your phone, once done get back to the main menu in recovery.
  11. Now once again select “Install > Choose Zip from SD card > Select file > Yes”
  12. This will flash the Gapps in your phone.
  13. Reboot your device.
  14. You should see the Android 6.0 Marshmallow running on your device in a while.
  15. That’s all!

First boot may take up to 10 minutes, you may not worry if it’s taking that much long. In case it’s taking too long, you may boot into TWRP recovery and wipe cache and dalvik cache and reboot your device as it may fix the issue. In case your device is having issues, you may return to your old system using the Nandroid backup or follow our guide here to install stock firmware.

Got any queries? Reach us out through the comment box below.

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