He has represented England through the age groups and this season his Aviva Premiership Rugby, LV= Cup and Amlin Challenge Cup experience was supplemented by a loan spell in the Championship with Doncaster Knights.
Although he paid tribute to the staff at Leeds who have helped him get started in professional rugby, Craig is excited by the challenge ahead of him at Franklin's Gardens.
"There are obviously a lot of people at Leeds who have helped me with my career and I owe them a lot of thanks," he said. "But now I'm massively looking forward to coming down to the Saints. The guys who I know here like Calum Clark and Scott Armstrong have told me that it's a great place to be, and visiting the club you can feel a buzz around the place, especially with the massive two or three weeks that are coming up. Hopefully I can help get the club to a similar place next year.
"The support you get with things like the conditioning is a massive help and it means that I can concentrate on nothing but developing my rugby. Hopefully the way I play will fit in with the way the team plays here. And with the full houses and great fans that follow the Saints it's a great place to play rugby."
Sempere is another newcomer who has played - and indeed scored - at Franklin's Gardens recently in last year's pre-season friendly against Nottingham.
That day the 27-year-old Spanish international was in the Green and Whites' number 15 shirt, but he is also comfortable at fly half and on the wing. In addition to his 22 appearances for Nottingham in the 2010/11 Championship Sempere has played Top 14 rugby for Montpellier and won 34 caps for Spain, scoring 22 tries.
"For me the Saints is one of the best teams in the Premiership," he said. "It is a great opportunity for me to show what I can do. I like to play with the ball in hand from everywhere, which is why I'm looking forward to playing in a team like Northampton. I enjoyed the game last August and the stadium seemed like a good place to play.
"Nottingham has been a good place to play and the club has good coaches and people there. It was my first experience in England and they made me feel very welcome. But the opportunity from Northampton was too good to turn down and I'm looking forward to playing there next season."
Director of rugby Jim Mallinder says that both players will be useful additions to the Saints squad next season.
"Our campaigns in the Premiership and in Europe have shown us the value of having a strong all-round squad, and with the World Cup coinciding with the start of next season we need players who can help us compete throughout next season," Mallinder commented. "James and Cesar have shown their quality in the Championship and in the games they have played against us in the last year, and we were impressed by what they can bring, not just in terms of playing ability but desire to succeed in a Saints shirt.
"We look forward to welcoming them to Franklin's Gardens during the summer."