The deal, signed with HBO, was announced by Channel 4 head Julian Bellamy at a Broadcasting Press Guild lunch today (27 January).
Both dramas will broadcast on the channel later this year - the first major new US drama commissions to debut on the channel since the underwhelming performance of Dirty Sexy Money last year. C4 director of television and content Kevin Lygo said last year that US series would now largely debut on digital channels E4 or More4.
True Blood is set in a world where vampires live openly in society. The 12-part series was adapted from Charlaine Harris' series of Sookie Stackhouse novels by Alan Ball, the creator of Oscar-winning film American Beauty and HBO's Six Feet Under, which was also shown on C4.
Generation Kill, which received its UK debut on satellite channel FX, is a seven-part series portraying the true story of the first 40 days of the Iraq war through the experiences of a group of young marines. It is based on the award-winning book by Evan Wright.
The series is overseen by the team behind acclaimed HBO drama The Wire, David Simon and Ed Burns and is a co-production between Skins indie Company Pictures and Simon's company Blown Deadline Productions. Simons' and Burns' earlier mini series, The Corner, had its UK debut on C4.
Gill Hay, who recently replaced Jeff Ford as head of acquisitions at Channel 4, said: "True Blood and Generation Kill are examples of HBO programming at its thought-provoking and challenging best; both series will find a natural home on Channel 4.”