In fact, N. T. Wright says, Paul is speaking here of the apostles, and pointing out that in their role as apostles, their activity is effectively God's righteousness (covenant faithfulness) in action ("we are ambassadors for Christ, God making his appeal through us. We implore you on behalf of Christ, be reconciled to God" - vv 20-21).
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Paul was positing that the people of such faith are vindicated when Messiah returns, being declared "righteous" (or in other words, vindicated for their stance), which is exactly the meaning of the Biblical term "justified", in N. T. Wright's view.
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N. T. Wright, who is one of the best-known advocates of the New Perspective on Paul, explains that although the "righteousness of God" and "righteousness from God" have been confused and conflated in the past, they are distinct concepts.