Dickson has been a mainstay of the Saints side since switching to the club from Newcastle Falcons in 2008.
He has racked up 250 appearances, with the 32-year-old reaching that milestone as a second-half replacement in the defeat to Leicester Tigers last time out.
But with Saints having signed South Africa No.9 Cobus Reinach for next season, Dickson was deemed surplus to requirements.
And he is now looking forward to the next chapter in his career, at Goldington Road.
“The move came about because of my brother (Karl),” Dickson explained.
“I was thinking about what I wanted to do in the next couple of years, whether that was continue playing or having a look at other things, and I was chatting with Karl who mentioned that Bedford would be the perfect fit for me.
“Karl spoke to (Bedford director of rugby) Mike Rayer, I then had a chat and arranged to come down to talk things through and after an hour of being at the club I made my mind up.
“Northampton will always be in my heart as it is a club I’ve played for for nine years but this is professional rugby and you have to look to the future rather than the past.
“I’m looking forward to the next chapter of my life with Bedford Blues.
“Bedford play a great brand of rugby here which really suits me.
“We played against the Blues a few weeks ago and at times they ran us ragged so I’m really excited about being involved.
“There’s a very talented backline at Bedford and I hope that I can pass on some of my experiences to these guys.”