Rawlings, who played alongside Simpson for 10 years at North Melbourne, has spent the past two seasons as the Kangaroos' senior recruiter and induction coach.
The role, which involves balancing the recruitment of new talent and the development of first-year players, was tailored for Rawlings, who took up a position within the Kangaroos recruiting department before retiring at the end of 2011.
A top shelf run-with midfielder and small defender later in his career, Rawlings played 245 games for North Melbourne, winning the best and fairest award three times, in 2004, 2006 and 2010 (equal).
Rawlings would have played a prominent role in the club's drafting this year, but he would now be expected to join West Coast immediately.
Meanwhile, the Eagles are unlikely to replace the position of strategy and innovations coach vacated by Phillip Walsh, with Simpson to oversee a team of assistant coaches on the same level.
As well as Walsh, who returned to Port Adelaide, the Eagles have lost assistant coaches David Teague and Scott Burns.
With Simpson a first-time senior coach, it was considered likely the Eagles would look to replace Walsh in the senior strategy and innovations role.
However, football manager Craig Vozzo told AFL.com.au that was now unlikely.
The Eagles have appointed past players Adam Selwood and Jaymie Graham as development coaches.
Twitter: @AFL_Nathan
