"This is monumental for a club like ours and a milestone in our history. We have just celebrated our centenary and to qualify for the new Championship, as SWALEC Division 1 West champions is difficult to put into words - it's just fantastic," explained TATA Steel chairman, Alf Hayes.
"The players and the coaches really deserve this because of the attitude, effort, discipline and commitment they have shown. They have been really professional all season and deserve all the credit.
"Our coaches, Lee Ratti, Matthew McCarthy and Mike Healey, have been superb. They have produced a side with no weakness - the forwards will win the game one week and the backs the next.
"We have worked our way up the Divisions and this title would have seen us promoted to the Premiership in years gone by. But the whole club is looking forward to competing and testing ourselves in the new Championship."
The fight for the title went right down to the finish and either TATA or Narberth could have emerged triumphant. As it was, TATA's five tries ensured they picked up the full five points they needed to clinch the crown.
Narberth did all they could do at Llanharan, winning 26-20 with four tries, but it wasn't enough after 22 rounds of matches and they ended up with 81 points to TATA's 82.
There was a tight first-half at Waunarlwydd which ended with the visitors leading 17-13. Prop Gareth Edwards and No 8 Rory Gallagher crossed for tries for TATA, but they gave away an interception score to Josh Hammett.
Half-way towards their goal of four tries at the break, TATA completed their mission with a second try from Edwards and a final flourish from wings Scott Robinson and Jordan Skidmore.
"This is the highest the club has ever reached in the SWALEC National League system and it is a proud day for us. We enjoyed consecutive seasons of promotion a few years ago, jumping from 3 West to 2 West and then 2 West to 1 West, and we've stuck fast for five seasons," said club secretary Elwyn Morgan.
"Now we will step into the unknown of the Championship next season and the only thing that is certain is it will be exciting and a bit more expensive. We will be travelling all over Wales and we'll have to pay for buses every other week."
Narberth had tries from Adrian Killa (2), Tom Bonnell and Johnny Morgan to thank for their bonus points win, 26-20, at Llanharan, but remained in second place. At the other end of the table, Ammanford finished bottom of the pile after suffering a 51-7 thrashing at the hands of fellow strugglers Bonymaen at Parc Mawr.
The hosts crossed for seven tries, five coming after the break, as they condemned the visitors to their 11th straight defeat, their last win came way back in November. Nathan Brooks and Richard Cunniffe both bagged braces for Bonymaen, with further tries coming from Stuart Allen, Richard Williams and Richard Brooks.
Tondu gave themselves the chance of finishing higher than 11th place after grinding out a narrow 19-18 win at Bridgend Athletic. The Waterwheelers crossed for the only try of the game through Paul Smithson, who also kicked a conversion and four penalties. Stephen Lewis kicked all 18 points for Athletic with six penalties.
Elsewhere, a Ricky Jones brace helped Carmarthen Athletic to a 27-18 win over UWIC, while Whitland slumped to a disappointing 21-8 defeat at home to Llangennech.