Lauren Shuler Donner, an executive producer on 'X-Men: Days of Future Past' in an interview said that Tatum was the one they've chosen as Gambit, citing his roguish charm, and experience with action as key factors in his casting. Not to mention that he's a southerner as well.
A key player in the X-Men universe, Gambit has been absent from the X-Men cinematic universe, save for Taylor Kitsch's portrayal of the character in 'X-Men Origins: Wolverine'. Earlier, Bryan Singer released a statement hinting that long time X-Men characters Gambit and Nightcrawler might appear in the next film in the franchise, X-Men: Apocalypse.
Gambit was created by writer Chris Claremont and artist Jim Lee, and his first appearance was in Uncanny X-Men Annual #14 which was first published in 1990. Although that was a brief introduction, he was fully incorporated into the Marvel Universe with Uncanny X-Men #266. Gambit has had two miniseries and starred prominently in the X-Force replacement title during the Age of Apocalypse, Gambit & the X-Ternals.
Gambit's main mutant ability is to mentally create, control and manipulate pure kinetic energy to his every whim and desire. Part of the Thieves Guild for most of his life, he's also a skilled fighter, good with a bo, and has masterful aim. Since his introduction, he has been a prominent member of the X-Men's main roster, having built a close relationship with fellow X-Man Rogue.
The character is also a fan favourite, ranking 65th on IGN's Top 100 Comic Book Heroes of All Time and is often featured in the animated adaptations of the X-Men, as well as video games based on the series.