The event aimed at comic fans was co-founded by Bryan Cooney who launched the show in 2002 as the London Expo. In 2004, it rebranded as London MCM Expo.
MCM also runs events across the UK in major cities such as Birmingham, Belfast, Glasgow, Liverpool and Manchester. ReedPop said that these events attract 300,000 pop culture fans.
It added that the takeover "will take effect immediately and its impact will begin to be seen and felt on all 2018 events". The next London event is taking place this weekend from 27 October.
Lance Fensterman, global head of ReedPop, said: "For nearly a decade I’ve watched with great admiration as the MCM brand grew in size, scale and quality, as well as in the hearts and minds of UK fans. I could not be more proud and humbled to team up with the MCM team to bring two world-class pop culture event companies together.
"The addition of the MCM brand extends the reach and influence of the ReedPop portfolio and further solidifies our place as the number one producer of fan events across the globe."