The campaign, "United against dementia", has its official launch on Monday evening, when a 90 second version of the ad will be shown on both channels simultaneously. The screening, at 8.55pm, will follow Coronation Street on ITV and Warship on Channel 4.
Both channels will run teaser spots over the weekend, while the ad itself will be preceded by a 10-second intro, announcing the partnership, which was brokered by media agency Hearts & Science.
The deal reflects the message of the campaign, created by McCann London, which calls on people to unite with their unlikely allies in the urgent fight against dementia, which affects people indiscriminately.
Vivienne Francis, director of marketing and external affairs at Alzheimer’s Society, said: "One person develops dementia every three minutes – yet extensive research has found that people don’t understand dementia and there’s a prevailing sense of hopelessness and inaction surrounding it.
"With McCann, and in partnership with ITV and Channel 4, we’re thrilled to launch a bold, striking and strong brand campaign that taps into post-Brexit societal divisions and turns up the volume on dementia. This campaign will position dementia as a salient issue, cement our new brand and move apathy to action."
Laurence Thomson, co-president and executive creative director at McCann London, added: "Seeing two rival broadcasters come together for such an important issue sets a brilliant example to us all."