The Stronger hitmaker is a huge fan of Seth MacFarlane's original animated comedy, and jumped at the chance to lend his vocals to the up-coming show.
The new series sees character Cleveland Brown move away from the neighbourhood he shares with bumbling Family Guy patriarch Peter Griffin.
West will play an aspiring rapper called MC Kenny West, and recorded his guest slot last week.
Executive producer Mike Henry tells People.com, "We knew Kanye was a big Family Guy fan because he invited Seth (MacFarlane) to his house a year or two ago.
Co-producer Richard Appel adds, "Before we came to the table ... there was only one line he didn't love, and he came up with another idea and in a completely modest, nice way said, 'Would you mind if I changed just this one line?'
"And our feeling was, how many raps have we written? One? And how many has he written? Be our guest."
The spin-off is set to air in the US in autumn, with West's slot slated to be shown in early 2010.