Nintendo will reveal the new Mario actor only in the credits of Super Mario Bros. Wonder
Charles Martinet has retired from the role of Mario after 32 years, which means that someone new will be taking on the responsibility in Super Mario B...

Charles Martinet has retired from the role of Mario after 32 years, which means that someone new will be taking on the responsibility in Super Mario Bros. Wonder. We still don't know who that person is, and we won't find out until October because Nintendo has revealed that we'll have to check the credits to find out.
"We're going to let it play out that way, and it will be within the credits," said Doug Bowser to IGN at Nintendo Live 2023 (as reported by Nintendo Life). "People will find out who the new person is at that time, but we don't plan on making an announcement ahead of time."
This means that the discovery of the new voice actor for Mario will be made by the person who first defeats Wonder. It's a race to uncover the new identity of the voice behind our favorite Italian plumber. There is also the new voice of Luigi to find, which Nintendo is also keeping secret. It's strangely mysterious, but Nintendo is working in its own unique way.
While Martinet has retired from the role of Mario, he hasn't completely distanced himself from the character. Nintendo has given him the job of Mario ambassador, a role that hasn't been fully explained yet and one that Martinet himself doesn't fully understand.
"As you may have seen in the news, I am now a Mario ambassador," said Martinet. "I'm not exactly sure what that means yet, I'm sort of not retired, but I am an ambassador and will learn over time. In the meantime... I am always an ambassador of Nintendo and Mario and all these events because I cherish every moment of it, and I hope your love for the games continues to grow like mine, so thank you very much."
Martinet is expected to have a video message with Shigeru Miyamoto in the near future, so we may receive clarity on what this role entails. Perhaps Martinet will introduce the new Mario voice actor, or maybe he will become the face of the Mario franchise at events - we will have to wait and see.
Another point Martinet mentioned when asked about his new role is that he has not retired yet, which many speculated after the announcement of his retirement from the role of Mario. Whether this means he will take on other voice acting roles in the future remains uncertain. Perhaps he will venture into unexpected territory and expand his skills, much like in Skyrim voicing Paarthurnax.
Super Mario Bros. Wonder will be released on October 20th, so we now have a little over a month before we find out who the new voice actor is.