To move your Apple Photos library to an external drive, quit Photos, drag the library from your Pictures folder to a Mac-formatted drive, then open the moved library and confirm Photos is using it. If you use iCloud Photos, set the moved library as the System Photo Library. Keep the drive connected whenever you use Photos, and keep a separate backup before deleting the original.

Prepare the external drive

Use a drive formatted as APFS or Mac OS Extended (Journaled). Apple advises against placing a Photos library on a drive used for Time Machine backups, a removable device such as a USB flash drive or SD card, or network or cloud storage. A dedicated external hard drive or SSD is a better fit. If the drive contains files you need, don’t erase or reformat it just to prepare for Photos; erasing a drive removes its contents. Apple’s guide to moving a Photos library

Before moving anything, make sure you have a separate backup of the library. A move is not a backup: if the external drive fails or is lost, the library on it may be lost too. Apple recommends backing up a library before using its repair tool and notes that libraries on external storage should be backed up with Time Machine on a different device. Apple’s Photos library overview

Move the library in Finder

  1. Quit Photos using Photos > Quit Photos. Wait for the app to close before moving the library.
  2. In Finder, choose Go > Home, then open Pictures. The default library is usually named Photos Library.photoslibrary. If you have more than one, check which one you use before moving it.
  3. Drag the library to the desired folder on the external drive. Keep the drive connected and awake while Finder completes the transfer; large libraries can take time.
  4. When the transfer finishes, double-click the library at its new location to open it in Photos.
  5. Browse several dates and albums and open a few photos and videos. Confirm the expected library is open before removing the original from the Mac.

Apple documents the Finder drag-and-open workflow. Do not open the library package to move individual files inside it: Photos manages its contents, and Apple warns against manually changing those contents in Finder. Apple’s move instructions

Set the moved library as the System Photo Library if needed

If you use iCloud Photos or want other Mac apps to access the library through the Photos picker, make the moved library the System Photo Library. In Photos, choose Photos > Settings > General, then click Use as System Photo Library if the button is available. The System Photo Library is the library that works with iCloud Photos and related sharing features; other libraries do not sync their changes through iCloud Photos. Apple’s library overview

If you turn on iCloud Photos for a newly designated System Photo Library, its contents may merge with the photos already in iCloud. Apple says those libraries cannot be unmerged after the new library uploads, so review the implications before enabling sync. Apple’s instructions for additional libraries

Keep the drive available and retain a backup

Connect and mount the external drive before opening Photos. Apple warns that if Photos cannot find the drive, it may create a new, empty library in the default Pictures location. That does not mean the external library has moved back; quit Photos and reconnect the drive, then reopen the library from its external location. Apple’s move instructions

After you have verified the moved library opens and contains the expected material, you can remove the old library from Pictures if freeing Mac storage is your goal. Keep a separate backup first, and be certain you are deleting the old copy rather than the library on the external drive. The external Photos library itself should not share its drive with a Time Machine backup. Apple’s library overview

If Finder reports a permissions problem, select the external drive in Finder and choose File > Get Info. Apple’s troubleshooting guidance says the Ignore ownership on this volume option under Sharing & Permissions may need to be selected; it may be unavailable if the drive format is unsuitable or the drive has been used for Time Machine and not erased. Don’t erase a drive with needed data just to change this setting. For a library that still misbehaves, back it up first and consult Apple’s Photos Library repair instructions.

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