The 20-year-old, who scored three goals in 23 appearances for Sky Bet Championship Bolton during the first half of the campaign, will hope to play a key role in the club’s push for promotion.
Announcing the deal on their official website, Blackburn said: “Rovers are delighted to announce that Newcastle United striker Adam Armstrong has joined the club on loan for the remainder of the 2017-18 campaign.
“The exciting youngster, who turns 21 next month, recently completed a loan spell at Championship side Bolton Wanderers and will now look to gain promotion to the second tier with Rovers.”
Armstrong joined Newcastle as a nine-year old and made his senior debut for the Magpies at the age of 17 years and 33 days.
He has since had loan spells at Coventry, Barnsley and Bolton.
Watford boss Javi Gracia does not think Abdoulaye Doucoure's form will be affected by his omission from France's latest squad.