The speaker is Cominius, the commander of the Roman army. The location of the speech is Rome, in the Capitol. Cominius is praising the actions of Caius Martius, who has just been given the third name of Coriolanus as an indication of the honor in which he is held after his actions in recent battles.
Cominius begins his monologue in recognition of Coriolanus's feats with the comment that "the deeds of Coriolanus should not be utter'd feebly." He goes on with the quote you cited, expressing his opinion that no single man in the world could "counterpoise" Coriolanus, meaning that no one is capable of equalling the fighting bravery and power exhibited by Coriolanus.
He continues with a history and description of the tremendous feats and victories Coriolanus has achieved.