The World Cup star's French side have said the 25-year-old has joined the Gunners.
Ospina had long been linked with a £3 million switch to North London, and has become the club's third signing of the summer, after Barcelona star Alexis Sanchez and Newcastle United fullback Mathieu Debuchy joined within the last few weeks.
The goalkeeper may not be the only arrival this weekend, with the club also close to agreeing terms for young Southampton right back Callum Chambers.
Sky Sports journalist Michael Bridge revealed that the player was on the cusp of a move after Nice manager Claude Puel confirmed the sale of his number one to Arsenal after the French club's friendly with Brentford on Saturday, telling press: "It's a good offer from Arsenal and he [Ospina] is a very good player."
Though there is no official word from Arsenal, Puel's admittance is a sure sign that the deal is done, with it likely the Colombian is currently engaged in photo shoots to announce his signing.
Ospina's arrival means that Wojciech Szczesny will have another young, hungry international goalkeeper to rival him for his spot, and though Arsene Wenger has said the 25-year-old will initially be backup to the Pole, he also admitted his belief that he is more than capable of becoming the Gunners first choice stopper.
"You know at the start Szczensy will be the No. 1, then again we'll be down to performances and, if Ospina shows that he is better, he will play," Wenger said.
Ospina enjoyed an excellent World Cup tournament in Brazil this summer, with Colombia reaching the quarter finals before narrowly losing out to the hosts. He has played 44 times for his country, and was at Colombian side Atletico Nacional before joining Nice in 2008, where he went on to make 177 league appearances.