The centre-half, one of four Addicks players named in the PFA League One Team of the Year, helped his colleagues secure the third-tier championship with a 2-1 victory over Wycombe.
Morrison has started every league game since joining from Sheffield Wednesday in July, and told the club's official website: "I don't think you could have written it any better for us - it's been perfect.
"We've worked hard all year, and when the boys look back at it, it's something that they'll remember for the rest of their careers. It might not happen again, so you have to make sure to enjoy every moment.
"I'm delighted because I couldn't have wished for the season to have gone any better both personally and for the team.
"Now we're looking forward to the last game of the season and it should be really good at The Valley."