For Windows – Keep Pidgin’s buddy list “always on top” of other windows for easy access to instant messaging without the hassle of switching windows. First, head to Tools → Plugins in the buddy list.
Scroll to the bottom, make sure Windows Pidgin Options is checked, then click it and Configure Plugin.
Next to Keep Buddy List window on top, click the menu and select Always. Hit Close to both windows and Pidgin should now remain on top of your other windows.