Oracle VM VirtualBox (formerly Sun VirtualBox, Sun xVM VirtualBox and innotek VirtualBox) is a virtualization software package for x86 and AMD64/Intel64-based computers from Oracle Corporation as part of its family of virtualization products

Since VirtualBox-4.3.8-4 PLD package, you can autostart guests:

1. edit /etc/vbox/autostart.cfg and fill which users may access the feature
2. as user, configure autostart dbpath:

   $ VBoxManage setproperty autostartdbpath /etc/vbox/autostart

3. modify VM to enable autostart of it:

   $ VBoxManage modifyvm <uuid|vmname> --autostart-enabled on

You can use VBoxManage list vms or VBoxManage list runningvms to figure out the UUID or VM name).

If you're using vagrant, then you can obtain uuid from id file:

$ cat .vagrant/machines/default/virtualbox/id
238dd504-f9f5-48c9-b214-cf64f16dc0ce

NB! VM needs to be stopped for modifyvm command to succeed.