The media specialist's move to align itself alongside IN's 90 creative shops is expected to boost its global reach and group billings, which last year were in excess of £71m.
Total Media's membership also ends a search by members of IN for an independent media agency to handle requests by clients to carry out media planning and buying activities.
Guy Sellers, managing director of Total Media, said joining IN will mean Total Media becomes a "vital link" in the growing global network of agencies.
New accounts generated through the network will be handled by Total Media's international hub in London, led by managing director Tom Laranjo. Discussions are already said to be underway about servicing the media requirements of a number of global fast-moving consumer goods brands in the Middle East, North Africa and Luxembourg.
IN claims to have the broadest geographical reach of any independent agency network, with member creative agencies in 91 countries.