Centre Piers O’Conor, 23, scrum-halves Andy Uren, 23 and Harry Randall, 21 and locks Joe Joyce, 25, and Ed Holmes, 23, have also all committed to three seasons with the Premiership side.
Thacker, 25, told BBC Radio Bristol signing was “an easy decision”.
“I strongly believe in the club’s vision and where we’re going,” he said.
“It is a club pushing in only one direction – and that is forward. It’s a great group and I am very excited for what we can achieve.
“We set our team goals but individually everyone has be improving day by day to push the team forward.”
“Pat has made no secret that that is what he wanted to do and that’s what we want to do,” said Morahan.
“The last two years have been very enjoyable.
“I saw the future would be pretty bright. You could see where the team wanted to go and we are stepping up to where we want to get to.”