Rashford, making his first England start since June last year, scored a fine free-kick to break the deadlock before rounding off the 3-0 victory after Phil Foden had doubled the lead.
The 25-year-old has endured a mixed 18 months since missing a penalty in the Euro 2020 final shoot-out loss to Italy and being targeted by racist abuse in the aftermath.
Rashford underwent shoulder surgery after the tournament and subsequently struggled for Manchester United, scoring just five goals all season and losing his place in Southgate's squad.
He did not kick a ball for England following the final until he scored just 25 seconds after coming off the bench in the team's opening World Cup win over Iran, having earned a recall following a strong start to the campaign.
His man of the match performance against Wales, where he came closest to opening the scoring in a quiet first half before arrowing in a free-kick and finishing through Danny Ward's legs to go level with the frontrunners in the race for the golden boot, was praised by United skipper Maguire.
"I am really pleased for Marcus. He showed he belongs on this stage," the England defender said.
"For the last year or so he has been in and out of the England team. I think he has really found his form again for Manchester United and he is a massive player for our club.
"Throughout a long career, you will always have ups and downs and it is all about how you bounce back when you are out of form.
"He has kept working hard and done that tirelessly. I can't speak highly enough of Marcus. He is a wonderful man and a great player."
As his club captain and England team-mate, Maguire revealed he has supported Rashford over his hard times, which continued when close friend Garfield Hayward died just days before the Wales game.
Rashford paid tribute with his goal celebration, with Maguire full of praise for how the forward has been performing of late.
"I speak to him a lot and I try to give him as much belief as I can," he said.
"But listen, Marcus is a fantastic player who has had a great career up until now. I think this last year has been difficult for him, but all good players rise to the top again.
"I think if he keeps his head down and keeps working hard - first and foremost for his club - then he will get opportunities for his country.
"Like I said, he showed he belongs on this stage. When he gets that opportunity with the confidence that he has, he is a threat to anyone.
"There's all types of things that you do. I am sure the coaching staff and everyone close to him try to help him.
"I am close to Marcus, a good mate of his on and off the field, the main thing is trying to get the belief back in his game.
"Marcus is a fantastic talent and you see it day in day out when you train with him. It was a matter of time until he got his confidence and form back.
"A career is a long time, over 15 years, there will be a lot of ups and downs. You've got to bounce back if you want to be successful."