It is not possible to add private key to Keychain, but you can store passphrase for private key in Keychain. On OSX, the native ssh-add command has a special argument to save the private key's passphrase in the OSX Keychain, which means that your normal login will unlock it for use with ssh. On OSX Sierra and later, you also need to configure SSH to always use the Keychain (see Step 2 below).
Alternatively you can use a key without a passphrase, but if you prefer the security that's certainly acceptable with this workflow.
#Step 1 - Store passphrase in the Keychain In the latest version of MacOS (12.0 Monterey), just do this once:
ssh-add --apple-use-keychain ~/.ssh/[your-private-key] Or in versions of MacOS older than 12.0 Monterey, use: