The 26-year-old left footed central defender has arrived on an initial loan, which Arsenal can convert into a permanent agreement in the summer.
Mari is experienced, even though many in England may not know a lot about him.
And Edu has spoken about the player's qualities.
"Pablo is an experienced player who will provide us with additional defensive quality," he said.
"We have been monitoring Pablo's career for a while and we are very pleased to have reached agreement with Flamengo for him to join us initially until the end of our season.
"Together with Mikel and his coaching team, we are all looking forward to seeing Pablo in an Arsenal shirt."