Poloskei arrives from MTK Budapest, the club Liverpool have a co-operation agreement with.
Poloskei becomes the fourth young Hungarian at Liverpool, joining compatriots Krisztian Nemeth, Andras Simon and Peter Gulacsi, all of whom also arrived from MTK.
"Liverpool officials have seen his performances a couple of times in the last two years and spoke highly of him so it was expected that he would get a contract," the midfielder's agent Tibor Pataky told the Hungarian press.
"He arrived at Liverpool with an injury but the club have been confident about their willingness to sign him, after some days Poloskei could begin training. Liverpool have the option to buy the player permanently after one year."