Manager Arsene Wenger has been under pressure to strengthen his squad after the club's poor start to the Premier League season and the 26-year-old striker could be the first of several signings before the transfer window shuts on Wednesday.
"We are delighted to have signed Chu. He will add true quality to our attacking forces and will be a valuable addition to the squad," Wenger told Arsenal's website on Tuesday.
Park, who played in the 2006 and 2010 World Cups for his country, scored 25 times in 91 appearances for Monaco. He replaced Manchester United's Park Ji-sung as South Korea captain earlier this year.
"I am very honoured and I feel very happy to be at Arsenal. It is a dream to be here and I am really proud to be an Arsenal player. Now I just want to show how good I am and prove myself," said Park, who will wear the number nine shirt.
"In my opinion this is a great club, now I have to show what I can do on the pitch. I will do my best, I will never give up, I will show heart, I will give everything and I hope [the fans] will support me."
Arsenal have managed just one point from their opening three league matches and have been hit by the sale of Cesc Fabregas to Barcelona and Samir Nasri to Manchester City since the start of the season.
The Gunners have also been linked with Werder Bremen and Germany central defender Per Mertesacker as Wenger tries to bolster a defence that was torn to shreds by United.
