Kiwomya, who has signed a three-year deal, spent last season on loan at Doncaster and helped them earn promotion from League Two under manager Darren Ferguson.
The 21-year-old never appeared for Chelsea's first team but won the FA Youth Cup and UEFA Youth League with the Blues.
He said: "I know the club came in for me a couple of times last season, but we could not get the deal done.
"It is nice to know they have had their eye on me for a while.
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10. Jairo Riedewald (Ajax) – 1.9
I think it was the right time to make a permanent move and show people what I can do
"It was a hard decision to leave Chelsea as I have been there from the age of 14, but I think it was the right time to make a permanent move and show people what I can do.
"I spoke to Jordan (Houghton) this week and he was saying that he would love to come back as he really enjoyed his time here."
Kiwomya added the vision of Ferguson was key for him deciding to join Doncaster.
Alex Kiwomya has joined Doncaster Rovers on a permanent deal
He added: "The main thing for me is getting consistent minutes on the pitch, the manager sees me as an important part of his plans so hopefully I can produce for him.
"I have got good vision and can link up play with my team-mates, I have got a lot of pace, so hopefully I can use that to create and score goals next season.
“The manager puts a lot of time into being able to change formations during a game, the players all work their socks off, so I am looking forward to being a part of that."