Wenger hopes Mertesacker will shine against Marseille in the Champions League on Tuesday, where a win would virtually guarantee progress to the knockout stages.
"Per is a good organiser," said Wenger. "He really understands the game and is an intelligent player.
"Physically, he's getting sharper in every game. He had no preparation for the season but now we look less nervous at the back and he contributes to that feeling."
And the Frenchman wants to see Mertesacker, 27, offer more of a threat from dead-ball situations.
He said: "Of course I expect some goals from him at set-pieces. In Marseille we had nine corners and from them, you expect to be a bit more dangerous. But if we beat Marseille, then it's another building block and we are virtually through to the next stage.
"We have been doing it gradually. Maybe people judged us too early. I am more than happy where we are now.
"Marseille will be difficult. But we are coming together nicely."