Bracken, 29, joins from Wasps while Hogan, 25, has left Connacht for the Memorial Stadium. Both have won caps for Ireland A.
Head coach Richard Hill, who has shaped Bristol into shock challengers for the Guinness Premiership this season, believes the duo are in their prime.
He said: "Peter and Ray will provide experience and know-how. Both have played European and representative rugby.
"They're approaching their peak and can play a big role for us. And, just as importantly, they really want to play for Bristol Rugby.
"They've watched what we've done here over the past few seasons and both want to play their part in taking us to the next level."