The defending English Premier League champions will have the option of signing Pato on a permanent deal in July, his agent Gilmar Veloz told SporTV.
The 26-year-old flew into London on Tuesday afternoon to undergo a medical and sign the contract, said to be worth about 200,000 US dollars a month.
Pato, who joined Corinthians from AC Milan for 15 million euros in January 2013, completed a two-year loan spell at Sao Paulo last month.
He enjoyed the most prolific season of his professional career in 2015 with 26 goals across all competitions.
Liverpool, Chelsea, West Ham and Tianjin Songjiang were also said to have shown interest in signing the Brazil international. Enditem