Put following gist to ~/Library/LaunchAgents, and then run: launchctl load /Users/your_name/Library/LaunchAgents/com.yourcompany.autossh.plist

com.yourcompany.autossh.plist

<?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>OnDemand</key>
    <false/>

    <key>KeepAlive</key>
    <true/>
    
    <key>RunAtLoad</key>
    <true/>
    
    <!-- Contains a unique string that identifies your daemon to launchd.
    This key is required. -->
    <key>Label</key>
    <string>com.yourcompany.autossh</string>

    <!-- Contains the arguments [to exec()] used to launch your daemon.
    This key is required.  -->
    <key>ProgramArguments</key>
    <array>
      <!--split your command. My command is: 
      /usr/local/bin/autossh -M 20000 -f -N -p 443 -g -C -c 3des -D 7070 name@you.ssh.server 
      change to your own.
      -->
      <string>/usr/local/bin/autossh</string>
      <string>-M</string>
      <string>20000</string>
      <string>-f</string>
      <string>-N</string>
      <string>-p</string>
      <string>443</string>
      <string>-g</string>
      <string>-C</string>
      <string>-c</string>
      <string>3des</string>
      <string>-D</string>
      <string>7070</string>
      <string>name@you.ssh.server</string>
    </array>
    
    <!-- low priority -->
    <key>Nice</key>
    <integer>20</integer>
    <key>LowPriorityIO</key>
    <true/>
</dict>
</plist>