“Ciaran is a very versatile player,” said Magpies manager Rafa Benitez. “As a left-footed centre-back, he can also play left-back and as a defensive midfielder.”
Clark was part of the Republic’s Euro 2016 squad and has scored 10 goals in 159 Villa appearances since making his debut in August 2009.
Former Wigan Athletic and West Ham United player Diame scored 10 goals in 45 appearances for Hull last season, including the winning goal as they beat Sheffield Wednesday 1-0 in the play-off final at Wembley.
“Everybody close to me knows how desperate I am to play in the Premier League again, but when Newcastle comes in for you it makes you think,” he told Newcastle’s club website.