Weir was the starting flyhalf for Scotland's final autumn Test, against Australia last November, but he was widely perceived to have dropped down the pecking order behind his Glasgow Warriors clubmate Ruaridh Jackson. That impression was reinforced by a shaky performance as a replacement for the Warriors against Toulon two weeks ago.
Scott Johnson, the interim head coach, explained that he was happy with the form and wider playmaking abilities of the former Celtic youth team midfielder. However, although Jackson does not even have the consolation of a place on the bench, Johnson hinted that Stuart Hogg, who returns to the side at full-back, could yet be the player to fill the 10 berth.
"It was a tough one," explained Johnson. "But we had a look and we quite like the skill set that Duncan brings to the team, stuff we don't have across the board. He's added some things to his game and we think that's a really good combination with [scrum-half] Greig Laidlaw.
"When I first coached against him I saw a fat little kid. Couldn't believe he was playing rugby at that level, in that position especially. His body's changed dramatically, he's deceptively quick and he's added a thrust in his attacking game. We want consistency now. If he can't do those things, he's not a 10, we expect him to boss people around."
Hogg had a couple of outings at fly-half on the Lions tour to Australia last year. Were Weir to pick up an injury against Ireland then Johnson would have the option of moving Laidlaw to stand-off, the position he filled throughout the 2012 Six Nations, but Hogg appears to be at the front of the queue. "We see Hoggy finishing a game at 10, we're happy to have him do that," said Johnson. "It's about time we had a look at that."
Asked about his selection, Weir said: "I can only take the opportunities that are put in front of me by the coaches. I've been on the bench for Glasgow, but coming on, I feel I've done my best to up the tempo and put in the points that the coaches want to see from their stand-off.
"Although the game time has been small, I feel that I've been doing that pretty successfully. I just have to grasp the opportunity, and look to boss the Scotland team to a nice victory on Sunday."
In another major selection surprise, Tim Swinson is chosen ahead of the Lions lock Richie Gray to partner Jim Hamilton in the second row.
Johnson, meanwhile, defended his decision to name Ryan Wilson, who has been preferred to Al Strokosch at blindside in the team, despite the fact the Glasgow forward is facing a serious assault charge.
Wilson appeared in court in December accused of attacking the Glasgow Hawks player Ally Maclay outside a fast-food shop and leaving him with a broken eye-socket. The prop Ryan Grant and the winger Sean Maitland are also accused in connection with the incident in October, but have yet to appear.
"You don't see me wear a wig, that's for someone else to do," said Johnson. "That's not my issue. My job is to pick a team from the players available and his form warrants that."
A group of Hawks representatives met senior SRU officials to discuss the matter at Murrayfield earlier this month, but were disappointed by the outcome.
"It had been hoped by Glasgow Hawks that a joint statement could be issued to reflect the general content of that meeting, unfortunately that has not been possible, said the Hawks president Chas Afuakwah. "Our concerns were that the union had failed to respond appropriately to the incident. Part of that failure is the union's failure to accept that a duty of care was owed by them to Ally Maclay.
"Throughout this sad episode Hawks have endeavoured to act in the best interests of Ally and the club game in Scotland. We have adopted a constructive approach in our dialogue with the Union, but it appears that the Union will not be in a position to decide on what further steps to take, if any, until the criminal process is concluded."