Jackson, 34, told BBC Radio Shropshire: "I had a choice to go to Scunthorpe, but I felt this was the right move."
The former Blackpool defender has joined Shrewsbury on a free under the 'Bosman' ruling.
Holt has signed a three year contract making the move from Forest after scoring three goals in their League One campaign last season.
But he spent the end of the season on loan alongside Jackson at Blackpool after becoming frustrated with limited first-team opportunities at the City Ground.
"The club's going in the right direction and I want to be part of it," Holt added.
His signing surpasses the club record of �100,000 paid for Aldershot's John Dungworth in 1979 and then matched by Mark Blake's signing from Southampton in 1990.
Shrewsbury boss Paul Simpson said he was delighted with the double signing.
"I think it shows the intent we've got for the season," he said. "I think it's a thank you to the supporters for the support they've given us with the season tickets.
"I think they're both experienced players, both know the leagues."
Simpson hopes to make one more signing by the end of the week.
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