Starting a guest operating system automatically is just very easy on VirtualBox and is handled nicely by a utility called VBoxManage. Below are the steps to start a virtual machine or a guest OS automatically.

Create a batch file and name it to anything you like e.g startvm.bat and insert the lines below to the batch file:

cd "c:\Program Files\Sun\VirtualBox"
vboxmanage startvm "virtual machine name"

Save the batch file and place it in the Startup folder.

That’s it, the virtual machine should start automatically every time you start the host machine.