Baldur's Gate 3 taps into Baldur's Gate 1 and 2 story wise, developer Larian has confirmed.
In a Reddit AMA, Larian boss Sven Vincke was asked whether there would be any connection between the story of Baldur's Gate 1 and 2 and expansion Throne of Bhaal, and Baldur's Gate 3.
Vincke kept his cards close to his chest, but did say this:
"We really don't want to spoil anything but we wouldn't call it Baldur's Gate 3 if there wouldn't be a link. Let me just say that we touch upon the story of BG 1 & 2 in meaningful ways, there are returning characters and what happened in BG 1/2/tob leads to what happens into BG3. You won't necessarily see that at the start of the adventure but you will quickly understand once you get further into the game."
Not only has there been an age between the last Baldur's Gate game and this new Baldur's Gate (Throne of Bhaal came out a sobering 19 years ago), but there may well be an age in their in-game timelines. Baldur's Gate 2 was set in 1369 DR (Dalereckoning). Baldur's Gate 3's story is said to take place immediately following the events of the Descent into Avernus prequel tabletop adventure, which itself is set over 100 years after Baldur's Gate 2, in the year 1494 DR.
So, while there may be links between Baldur's Gate 3 and the original games, and even returning characters, it's clear Baldur's Gate 3 is not a direct sequel. As long as Boo turns up, I'll be happy.
For more, do check out Chris Tapsell's wonderful Baldur's Gate 3 preview. The game is expected to hit Steam Early Access by the end of 2020.