The Londoners, who have won just three of their last 33 matches, will be playing in the third tier of English football for the first time in 28 years next season.
The financial meltdown of their dramatic decline two years after being a Premiership club has led to 30 members of staff being under threat of redundancy and put the future of manager Phil Parkinson in doubt as his team have managed just three wins in the 25 games he has been in charge.
Blackpool themselves had been flirting with relegation but made their Championship status safe with this point despite being out-played for most of the match.
Two goals in a minute immediately after half-time gave Charlton the advantage.
Deon Burton put the Londoners in front with a looping header and 17-year old Jonjo Shelvey scored the second with a sweet strike from 10 yards.
Blackpool were given a lifeline back into the match when Dudley Campbell was felled in the area and he got up to stroke home the penalty to reduce the arrears.
Charlton's dismal season was summed up in injury time when substitute Lee Hughes, who had only been on the field two minutes, scored the equaliser which ensured the Addicks were relegated.
The only bright spot for the home side was the performance of 17-year old Shelvey and another teenage striker Tamer Tuna became the 37th player to be used this season - a club record.