The 27-year-old striker has been linked with a switch to the Madjeski Stadium for some time but has now completed the formalities of a deal that is believed to allow him to stay with the Royals until the end of the year.
Mauricio Pochettino has spoken in recent weeks of his desire to allow Sharp the chance to play first team football elsewhere, as he remains out of his plans.
Sharp was signed by Adkins for Saints for £1.8m in January 2012 and scored nine goals to help the club to promotion to the Premier League.
However, Adkins largely overlooked Sharp in the Premier League, recruiting Emmanuel Mayuka and switching formations to play just one up front.
Now though the pair are to be reunited at Championship level at Reading.