Allison worked as development coach at the Swans for nine years that largely coincided with Roos' 2002-10 coaching reign.
A North spokesman confirmed on Wednesday Allison was leaving to join Roos at Melbourne.
Allison joined North in 2010 and has worked predominantly with the Kangaroos' forwards in his time at Aegis Park.
Melbourne is expected to officially announce Allison's appointment shortly.
Twitter: @AFL_Nick