Norwich snap up defender from 'Pool on a free
The 29-year-old leaves the Canaries' League One rivals after six years and over 300 appearances at Victoria Park, where he was club captain.
Nelson said: "When you come and look around the place, it sells itself.
"This is a massive club with one of the best stadiums in the Championship, let alone League One."
Nelson said there had been interest from the Championship before he agreed the switch to Carrow Road.
"Talks went on but there was no offer on the table as such," he said.
"In the end I had to make a decision and I think I have made the right one."
Elsewhere, Oldham have completed the signing of former Bristol Rovers defender Joe Jacobson on a two-year deal.
The Wales under-21 international, 22, was released by the Pirates at the end of the season after making 84 appearances since joining in 2007. Jacobsen started his career at Cardiff and had a loan spell at Accrington.
"Oldham are a big club and new manager Dave Penney has a reputation of getting the best out of players — that suits me fine," he said.
Huddersfield Town have signed striker Robbie Simpson from Coventry City for £300,000, subject to a medical. The 24-year-old has agreed a three-year deal.
Huddersfield manager Lee Clark said: "I'm absolutely thrilled to have Robbie Simpson moving to the club.
"He is a young, hungry player who wants to get better and that is exactly what I want."
Robbie Simpson
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