The service's updated FAQs note that users whose devices have those operating systems "can no longer create new accounts, nor reverify existing accounts" after that date, the Efe news reported.
WhatsApp, which is owned by Facebook, said it expected a limited impact from the change since it would only affect users who had not purchased a new phone or updated their operating system in more than six years.
In fact, users whose devices have older operating systems are already unable to create new WhatsApp accounts or reverify existing accounts, but the company does allow those who already have the app on their phones to continue using it.
Menlo Park, California-based WhatsApp said that "you'll no longer be able to use all Windows Phone operating systems after December 31, 2019, and WhatsApp might not be available in the Microsoft Store after July 1, 2019."
This change is expected to have even less of an effect on users since only about 0.24 per cent of mobile phones around the world, according to Statcounter, use a Windows operating system.
The 0.24 per cent figure includes all versions of the Windows operating system, including the more recent Windows 10 Mobile, so that the number of current Windows Phone users is insignificant.
WhatsApp recommended using Android 4.0.3 or later; iOS 8 or later; and certain phone models with KaiOS 2.5.1 or later, including the JioPhone and JioPhone 2.
( With inputs from IANS )