To move a chat from WhatsApp on iOS, open the Contact Info or Group Info page in WhatsApp, tap Export Chat, then choose Telegram in the Share menu.
On Android, open a WhatsApp chat, tap ⋮ > More > Export Chat, then choose Telegram in the Share menu:
WhatsApp for iOS also lets you export chats directly from the chat list. Swipe left on a chat, then choose '…' > Export Chat.
Messages will be imported into the current day but will also include their original timestamps. All members of the chat on Telegram will see the messages.
Starting today, everyone can bring their chat history – including videos and documents – to Telegram from apps like WhatsApp, Line and KakaoTalk. This works both for individual chats and groups.