Wrexham boss Phil Parkinson commended his side for making history after they completed a hat-trick of promotions to seal a place in the second tier.
Saturday’s 3-0 home defeat of Charlton means the hosts have now sealed their third promotion in as many seasons.
The Red Dragons started brighter and had a two-goal lead inside the opening 18 minutes.
Ollie Rathbone found the back of the net first with a sensational strike from outside the box and Smith soon followed with a volley from close range.
Charlton’s best chance came on the half-hour mark, but Tennai Watson’s chance was saved by Arthur Okonkwo.
Smith got Wrexham’s third and final goal in the 81st minute, heading in from a cross.
“The key for me today is how we have done it,” said Parkinson.
“The performance today was really controlled and at times high quality, I am so pleased with that.
“Getting over the line in football is really hard, and having the control and mentality to produce performances of that standard in such a pressured game is enormous credit for everybody.
“Everybody has been talking about making history all season, and right at the start, we knew what was at stake, and nobody can ever take that away from us.
“Every supporter, the owner and everybody connected with the club, such as the staff and players, these medals mean a lot and they’re worth a lot.
“We created history today with these three promotions, and hard work has to go in.
“I go into every season thinking we can go in and achieve promotion, but to do it is amazing.
“The trajectory has been a rapid one. We have had to evolve continually, and I think this season we have evolved as a team.”
The defeat ended Charlton’s hopes of automatic promotion but they are assured of a place in the play-offs.
Addicks boss Nathan Jones said: “It was a tough one.
“Firstly, congratulations to Wrexham, they did the basics far better than us and they probably outworked us.
“We came up against a good side today who are at the top of their game, and they have a fantastic squad.
“It has been a difficult one to take but let’s look at the positives. We are on a fantastic run, and we have secured a play-off place.
“It was a tough run to keep going and get second but we had a really poor November, which cost us. But we are still in a wonderful place and we have to finish the season strongly.
“The first goal is important, and we didn’t close the ball down well enough.
“If we can defend the set-plays and stop Smith and defend crosses, then you have a hell of a chance because that is what they do.”
