The 25-year-old former Coventry frontman has been called up by manager Giovanni Trapattoni with West Brom's Shane Long likely to miss out because of a knee injury.
Best has been in superb form for the Magpies, and his partnership with Demba Ba has been a key feature of the club's rise to third place in the Barclays Premier League table.
A statement released by the Football Association of Ireland said: "The Football Association of Ireland today confirmed that Newcastle striker Leon Best has been called up into Giovanni Trapattoni's squad to face Estonia in the Euro 2012 play-offs on November 11 in A le Coq Arena, Tallinn, and November 15 in Aviva Stadium, Dublin."
Best was not included in the initial 26-man party announced by Trapattoni last week, with the fit-again Robbie Keane, Kevin Doyle, Shane Long, Simon Cox and Jon Walters staffing the striking department.
However, West Brom's Long was named despite battling against a knee injury suffered during the 2-1 derby victory at Aston Villa on October 22, and the Baggies have admitted he has little or no chance of being fit.
Manager Roy Hodgson said: "Shane is not fit to play. The two doctors are in contact with each other and the Irish doctor knows that he is making good progress and we are working hard with him.
"But he is way off being fit to play a football match.
"If they want to prove that by inviting him over and sending him back again, that's okay with me.
"But there is no way, unfortunately, he will be fit to play for us at the weekend or for Ireland.
"In fact, there is a lot of work to be done if he is going to be fit to play after the international break.
"It is going to take some time to heal. The initial suggestion was six weeks and Shane would like it to be quicker than that - but it certainly isn't going to be two weeks."
There has been a clamour in Ireland for Best's inclusion anyway following his impressive start to the new campaign.
He scored three times in as many league starts at the beginning of the season, and while he has not added to his tally in his last five appearances, manager Alan Pardew has been delighted with his contribution alongside Senegal international Ba, whose hat-trick secured a 3-1 win at Stoke on Monday night.
However, when asked about the Newcastle player last month, Trapattoni said he was monitoring him, but wanted to see him working harder for his team, something which mystified Pardew.
He will now get the chance to impress the Italian all over again as he attempts to add to his seven senior international caps to date and put himself in contention for a trip to Poland and the Ukraine next summer if Ireland can ease their way past the Estonians.
Trapattoni fielded his first-choice pairing of Keane and Doyle in Andorra last month, and turned to Long's Baggies team-mate Simon Cox to partner the Wolves man against Armenia four days later with the skipper sidelined by an adductor muscle strain.
Best will meet up with the squad when it assembles in Dublin next week, with a question mark also hanging over Sunderland defender John O'Shea.
The 30-year-old has been ruled out of Sunderland's league trip to former club Manchester United on Saturday with a recurrence of the hamstring injury which wrecked his pre-season, and manager Steve Bruce admits he is unlikely to be fit for the game in Tallinn.
Bruce said: "He's certainly got no chance for Saturday, and looking at the first game for Ireland next Friday, I would have thought he's a huge doubt for that as well, which is a shame for the lad.
"It's typical of the luck he's had, unfortunately, since he's been here. They are probably the two biggest games he has been looking forward to.
"He might have a chance for the second one, but certainly I would have thought the first game would come a little bit too quickly for him."