The Irish arrive in Cardiff as marginal title favourites ahead of France but having suffered a major blow after British and Irish Lion Furlong was ruled out due to a calf injury.
Australia-born Bealham will make his full debut in the championship at the age of 31 by deputising at tighthead on the back of some standout displays for Connacht and a series of impressive Test outings from the bench.
Farrell is hopeful Furlong will be back in contention for next week’s round-two clash with France but has full faith in his understudy, who has won 23 of his 27 international caps as a replacement.
“He’s not quite ready,” Farrell said of Furlong. “In fact, he’s progressing pretty well but he’s not quite there yet.
“He could possibly be there in the next few days or week or whatever, but we just think that Finlay deserves it as well.
“He’s playing some outstanding rugby at this moment in time. The last game he played, he scored a hat-trick, he’s scrummaging very well, so he deserves a start.
“Tadhg will keep working away to hopefully be fit for the French game.
“Coming back from the autumn, or any camp he’s been in with us, he (Bealham) has had that trust.
“He’s a massive personality within our squad, he’s very popular, but coming out of the autumn and how that translates, going back to Connacht and his performances since then has been top-drawer.”
Farrell’s maiden selection of the tournament includes Ulster centre Stuart McCloskey retaining his starting spot from the autumn ahead of Bundee Aki to make his first Six Nations start since his Test debut seven years ago.
Farrell is happy the Principality Stadium roof will be closed for the encounter as he is eager for his in-form team to handle the loudest possible atmosphere.
However, the Englishman laughed off claims from rival head coach Warren Gatland that the clash is a “free hit” for Wales due to Ireland’s position at the top of the world rankings.
Farrell said: “A free shot in Test match rugby? Where do you get them from?
“We’d love to be able to buy one of those. Maybe I’ll buy him a free shot after the game.
“But there’s absolutely no doubt that Warren will expect his side to win… and so do I. I expect our side to win.
“His past record shows what he’s about in this competition. Finding a way to win has always been key to those teams, and we’re very aware of that.”