The Egyptian international spent the first half of the current season with the Yorkshire outfit, making 23 League appearances before his parent club exercised the recall clause in the deal on January 16.
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The Tigers have also secured short-term deals for fellow Egypt internationals Gedo and Ahmed Fathi from Al Ahly.
Elmohamady tweeted his delight at his compatriots signing: "Glad to have my compatriots, Gedo and Fathi at Hull, Welcome new Tigers!"
The right-sided player's only outing for the Black Cats this month was as a stoppage time substitute in the Wearsiders’ 3-2 victory over Wigan.
Fathi previously played in the Premier League for Sheffield united, but only made three appearances in an 18-month spell at Brammall lane. The midfielder, who can also feature in defence has 91 caps for Egypt.
Gedo, a striker, moves with Fathi from Al Ahly and was the top scorer at the 2010 Africa Cup of Nations, which the Pharaohs won.