How to run Mac OS X application at system startup

1. Create a text file with .plist extension (for example, com.myname.myapplication.plist) with the following content:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>com.myname.myapplication</string>
    <key>ProgramArguments</key>
    <array>
        <string>/Applications/My Application.app/Contents/MacOS/my_application</string>  
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>KeepAlive</key>
    <false/>
</dict>
</plist>

2. Replace strings in bold with your application id (can be any unique string) and path to your application executable.

3. Put it to /Library/LaunchAgents directory:

sudo cp com.myname.myapplication.plist /Library/LaunchAgents

4. Change file permissions to 644:

sudo chmod 644 com.myname.myapplication.plist

More information:

Introduction to System Startup Programming Topics

Technical Note TN2083: Daemons and Agents

launchd.plist(5) Mac OS X Manual Page

launchctl(1) Mac OS X Manual Page