The Sydney Roosters centre flew out of the line in the eighth minute to put a shot on Queensland's fullback while the Maroons were on the attack after their first try at Accor Stadium on Wednesday night.
Walsh had been targeted by the Blues defence early and lay motionless on the ground, apparently unconscious, after receiving the hit from Suaalii.
Queensland teammates, and then staff, attended to Walsh on-field.
Reece Walsh receives treatment after being floored late by Joseph-Aukuso Suaalii. (Mark Evans/AAP PHOTOS)
Play initially continued downfield but was eventually brought to a halt by referee Ash Klein, who pulled Suaalii and new Blues captain Jake Trbojevic aside.
"That is a very dangerous action, there is direct contact to the head. You're off," the referee said to Suaalii.
Walsh was able to regain his footing and walk from the field.
He was initially ruled to have been suffering category-one head injury symptoms so was out of the remainder of the game, though encouragingly passed a concussion test in the sheds later in the first half.
Suaalii's send-off meant the Maroons became the first team permitted to activate their 18th man mid-way through an Origin game since the rule was introduced in 2021. Dolphins forward Felise Kaufusi joined Billy Slater's bench.
The Nine Network's broadcasters crossed live to Slater shortly after Walsh was ruled out, with the Queensland coach tight-lipped on the incident.
Asked for his opinion on the rugby union-bound centre's move, the coach said: "You probably don't want to know that."
Suaalii became the sixth player in Origin history to be sent straight from the field, and the first since Walsh and Jarome Luai who were dismissed for headbutting one another in the dying minutes of game two last year.
The next-earliest player dismissed from an Origin game was Craig Greenhill, given his marching orders for a high tackle in the 62nd minute of game two, 1996.
The shot cast extreme doubt over the Blues' hopes of starting the Michael Maguire-era on a winning note.
Suaalii's dismissal also brought attention to Maguire's decision not to carry an outside back on his bench - a selection call that sparked debate in the lead-up to Origin I.
The Blues chose versatile Matt Burton as their 18th man, behind four specialist forwards on the bench proper.
Second-rower Liam Martin initially defended on the right edge to cover for Suaalii but Stephen Crichton shifted from the left to the right later in the first half to sure up the edge.
PLAYERS SENT OFF IN AN ORIGIN GAME:
* Craig Greenhill (QLD) - High Tackle - 62nd minute, Game II, 1996
* Gorden Tallis (QLD) - Referee Abuse, 71st minute, Game I, 2000
* Trent Waterhouse (NSW) - Striking, 78th minute, Game III, 2009
* Jarome Luai (NSW) - Headbutt, 79th minute, Game II, 2023
* Reece Walsh (QLD) - Headbutt, 79th minute, Game II, 2023
* Joseph Suaalii (NSW) - High Tackle - 8th minute, Game I, 2024
