Both Italy internationals, Borriello has swapped Roma for a Premier League survival scrap, while Nocerino has traded AC Milan for the east end.
Seven-cap Borriello, 31, is a striker with close to a hundred career goals to his name, accrued at the likes of Milan, Juventus, Genoa and Roma.
He joined the capital club in the summer of 2010 amid rumours of interest from Manchester City, while he won the title with Juventus during a 2012 loan spell.
His signing was announced after that of Nocerino.
Nocerino, 28, has also been drafted in to help the Hammers in their battle to earn Premier League survival, with Sam Allardyce's men currently in the relegation zone.
Capped 15 times by Italy, Nocerino is known to English fans for scoring a penalty against England at Euro 2012.
The ex-Juventus and Palermo man has been a bit-part player this season having previously been a key man for the club he joined in the summer of 2011.
The duo's arrival was announced on West Ham's official website the day after Leeds confirmed they had turned down an offer from the Hammers for leading scorer Ross McCormack.