To move photos library to external hard drive, you simply move the entire Photos Library file rather than individual images. This keeps all your albums, edits, and metadata intact while freeing up space on your Mac.
Before you move your photos library to an external hard drive
Critical preparatory steps come first to prevent data loss. Quit the Photos app entirely, do not just close its window. Check that your external drive is formatted as APFS or Mac OS Extended (Journaled) by opening Disk Utility. Do not use a drive that is also used for Time Machine backups, as this can cause conflicts and data corruption. Avoid storing your library on removable storage like SD cards or USB flash drives, or on network or cloud-based services, due to potential data loss and poor performance. In the Finder, select your external drive, press Command+I to open Get Info, and ensure "Ignore ownership on this volume" is checked.
Locate and copy your Photos Library file
In Finder, open your home folder and navigate to the Pictures folder. Look for the file named "Photos Library.photoslibrary". If you have referenced files, photos stored outside the library bundle, they will not move with the library and will not sync with iCloud Photos. Before copying, open Photos, select File > Consolidate to bring those files into the library. Then drag the "Photos Library.photoslibrary" file from the Pictures folder to your desired location on the external hard drive. The copy may take from minutes to hours depending on library size; do not interrupt it. If you also need to archive a cloud collection, you can download all photos from Google photos to external hard drive for a complete local backup, and then transfer Google photos to external hard drive to keep everything in one place.
Open and verify the library on the external drive
After the copy finishes, double-click the Photos Library file on the external drive. The Photos app will launch and display your library. Browse through albums, individual photos, and edits to confirm everything is intact and accessible. If you encounter missing content, recheck the copy process before proceeding.
Set the new library as your System Photo Library
If you use iCloud Photos or need the library accessible by other applications, you must designate the external library as your System Photo Library. In Photos, go to Settings > General and click "Use as System Photo Library". This ensures iCloud syncs correctly and other apps can find your photos. If you ever need to switch between libraries, quit Photos, hold the Option key while reopening it, and select the desired library from the dialog box. You might also want to organize Google photos by creating albums and folders within the library once it's on the external drive.
Delete the original library to free up Mac space
Once you have confirmed the library works correctly from the external drive, you can reclaim space. Drag the original "Photos Library.photoslibrary" from your Mac's Pictures folder to the Trash, then empty the Trash. Be warned: the external drive must always be connected and available whenever you open the Photos app. If you open Photos without the external drive connected, it will create a new, empty library in the default location on your Mac.
