The Glasgow number 10 has played just 12 minutes of the championship, coming off the bench in the defeat by Wales.
But in the absence of the injured Finn Russell, he has been preferred to Peter Horne, who impressed against France.
"It's tough on him not being selected but it's an opportunity for me," said Weir, who wins his 23rd cap in Dublin.
"The coaches have given me confidence this week. They have watched my Glasgow footage and are happy where I am and my development over the last month or so.
"I feel confident in my game at the minute and just need to back it up come Saturday.
"It is a huge honour getting back into the side. I have been here training, so I know the calls and structures, so it is not being thrown in to the deep end as I have been here throughout the championship."
With Russell still going through concussion return-to-play protocols after receiving a head knock five minutes into the France game, Cotter had the option of continuing with Horne - who he called "probably a 12-10 rather than a 10-12" - after he stepped into the fray with aplomb.
"I was just hugely proud of his performance," Weir said of his Glasgow team-mate. "A guy who has not run a rep pretty much the whole tournament at 10 steps up and shows how natural a ball player he is.
"It was great for me to go on and see him run the attack. Being a playmaker at 12, he is always chatting and orchestrating play anyway."
Having played second fiddle to Russell at club level as well as with the national team, being left out of the match-day 23 for the last two Tests against Italy and France has allowed Weir more game time with Glasgow.
He duly delivered two Pro 12 man-of-the-match displays against Newport Gwent Dragons and Cardiff Blues.
"I have been getting a run of games so I feel confident in my form," he added. "Moving onto the ball you have to make better decisions when you have a run of games going. I feel really excited about the opportunity."
Weir will be tasked with directing an attack - featuring Glasgow team-mates Stuart Hogg, Tommy Seymour and Alex Dunbar - that has produced eight tries so far, only one less than Scotland's best Six Nations tally of nine in 2000.
But he is under no illusions that the keys to a third straight victory, which would match Scotland's best-ever Six Nations tally and likely equal their joint-best finish of third, may lie elsewhere.
"Our defence and set-piece will be huge again," he added.
"That will be at the front of our minds. Ireland are playing with a lot of width in their attack so we have to be cautious of that and get our spacing right in defence and shut things down and not be too aggressive at times.
"Once we get the ball we have to play at a tempo they can't live with."

City supporters' organisation the 1894 Group, which has criticised the club's ticket prices, said it was a "step in the right direction".
But, in a statement, the group added: "It's vital we keep the pressure on the club and use our collective voices."
Swansea are also among the Premier League teams to cap their prices.
West Ham, meanwhile, will lower season-ticket prices for their move to the Olympic Stadium for 2016-17.
Liverpool cancelled plans to introduce a £77 ticket next season after thousands of fans walked out of Anfield after 77 minutes of their game with Sunderland in February.
In March, all Premier League clubs agreed to cap the price of tickets for away supporters at £30.
Fly-half Duncan Weir says he is ready to repay the confidence of the Scotland coaches as he prepares for a first Six Nations start of the year in Ireland.
[NEXT_CONCEPT]
Manchester City will freeze season-ticket prices next season, matching the commitment made by Manchester United, Arsenal and Chelsea.