Biggar's 12th cap doubles up as a first Six Nations appearance, and it will be opposite a player widely viewed as favourite to be the British and Irish Lions fly-half in Australia later this year.
Whoever comes out on top individually looks set to have a pivotal say regarding the result of an opening weekend encounter between two closely matched teams.
"I could sit here all day and say how good a player Sexton is," Biggar said, ahead of the Millennium Stadium clash.
"I am really looking forward to going up against him. I have played against him many times, and he's right up there on top of his game at the minute.
"It is a real challenge and privilege to play against him when he's playing as well as he is.
"He is a great player and he has got great players around him, which is always nice for a 10. It makes your job easier when you have got centres like (Gordon) D'Arcy and (Brian) O'Driscoll outside you.
"But we have got a pretty good back line with the likes of Jamie Roberts and Jonathan Davies. They have got pedigree as well. It's exciting."
Wales will launch their Six Nations title defence on the back of seven successive defeats, but they have beaten Ireland three times in a row and suffered just one championship defeat at home against all opponents since March 2010.
"We had a poor autumn - there is no hiding away from it," Biggar added. "But this is a new campaign with new strategies in place, and it's something we are looking forward to.
"We have got to do the simple things well. International rugby is about doing that, about making your set-piece and ensuring your kicking game and defence is in order.
"You get those three things right, and you stand a good chance of winning games of rugby."
Biggar will line up in a team containing 10 survivors from the side that started last season's Six Nations title and Grand Slam-winning campaign by beating Ireland.
But while familiar faces like Leigh Halfpenny, Mike Phillips, Gethin Jenkins, Adam Jones and skipper Sam Warburton all feature, there is also a Wales debut for 28-year-old Newport Gwent Dragons lock Andrew Coombs.
Coombs' elevation to Test match status comes less than three years after he made his Dragons debut, and he only recently switched positions from back-row to lock when the Dragons were hit by injuries.
Coombs will partner fit-again Ian Evans at lock, but Wales remain without injured second-rows Alun-Wyn Jones, Bradley Davies and Luke Charteris.