The 25-year-old played with Rioli at WAFL club South Fremantle, and he hopes the duo can link up again in Eagles colours.
“I’ve known Willie for a long time,” Kelly said.
“When I started off at South Fremantle, he was there as well. I played with him for a year and a half before he went back to NT.
“I’m excited about being his teammate, and I’m here for him and everything that he’s going through.”
Kelly’s arrival has given West Coast’s 2020 flag hopes a massive boost.
The skilled midfielder will join Elliot Yeo, Luke Shuey, and Andrew Gaff in a star-studded on-ball division.
With ruckman Nic Naitanui giving them silver-spoon service, West Coast’s midfield has the potential to become the best in the AFL.
The Eagles had to give up picks 14, 24 and 37 in this year’s draft as well as their first-round pick in 2020 in order to land Kelly.
The Eagles received Geelong’s pick 57 this year and a third-round selection in 2020.
The price to land Kelly was hefty, but Eagles coach Adam Simpson said it was well worth it.
“We’re ecstatic,” Simpson said. “When you reflect where we’re at as a club, we’ve spent the last three or four years through the draft. We’ve got some good young talent coming through.
“So we understand to keep our list together you have to give up some picks.
“We’ve been able to get someone like Tim into the club and hold onto some players, which is important and it’s made our list stronger.
“We can continue to strive for the ultimate, but it doesn’t guarantee anything.”