Slater had been with Leicester Tigers since 2010 and it appeared he would be heavily involved in an eighth season at Welford Road with the new campaign just around the corner.
However, Gloucester showed major interest in the 29-year-old and they managed to secure a deal on Monday that saw England international Jonny May head in the opposite direction to his compatriot.
The Cherry and Whites' new arrival admits it was a slight shock to hear of interest in August but he was more than happy to accept this new challenge when the opportunity arose.
"It was a surprise really to be honest with you because I don't think I've ever heard of summer transfers in rugby," Slater told Gloucestershire Live.
"My initial reaction was I've only got one year left of my contract, it's probably not going to happen but then, as it became more clear and David Humphreys made a massive effort in getting me down here and speaking to me, I think for me I needed to step out of my comfort zone at Leicester and this is a new challenge."