After spending seven years at Sunderland - with the Black Cats suffering two successive relegations seeing them demoted from the Premier League to League One - O'Shea has now taken the decision to depart and has joined the Royals on a one-year contract.
The Championship club revealed the signing of the 37-year-old centre back on their official club website on Wednesday evening, with Royals boss, Paul Clement saying: “John has played and won at the very highest level – he has won five Premier League titles, been part of a European Cup-winning side and earned 118 caps for his country.
"He will bring us fantastic levels of experience and proven leadership qualities.
“We looked very carefully at John’s recent playing statistics and he played a total of 40 games for Sunderland last season; he is still incredibly fit and a hugely motivated individual. So we look forward to him being a big contributor out on the pitch next season.”
This will not be the first time O'Shea has worked under Clement either, with the Irishman playing under the Reading manager during his time as part of the Ireland under-21 setup.