The deal includes pouring rights for the firm’s brands at Ashton Gate, the home ground that the rugby team shares with Bristol City FC.
It will sponsor the man of the match award for rugby matches and have pitchside, website and programme advertising. Thatchers will also appear on the shirts of the Bristol women's team.
Andrew Billingham, chief executive officer of Bristol Sport, said: “"Thatchers’ ciders have long been a favourite at Ashton Gate.
“We're pleased to see that relationship develop and extend to Bristol Rugby's iconic home and away shirts.
"With Bristol back in the top flight and the new Ashton Gate stadium on the brink of completion, it's a hugely exciting time for the club and our commercial partners."
Martin Thatcher, fourth generation cidermaker at Thatchers, added: "We wish everyone involved with Bristol Sport and the associated clubs a very successful season and we look forward to sharing some great times with them."