Tight end Eric Saubert executed the game-winning two-point conversion for Seattle.
Seattle engineered a stunning fightback to overcome the Rams in overtime, securing their place in the NFL play-offs.
Rallying from a sixteen-point hole in the final period, the Seahawks emerged victorious 38-37 at home, registering their fifth straight victory.
While the Rams had already secured a playoff spot earlier on game day, the Seattle team booked their return to the postseason after a 24-month absence.
With this result, the Seahawks have taken over their Conference race with a twelve and three record, supplanting the Los Angeles, who dropped to the number five playoff position with an eleven and four standing.
Quarterback Darnold had two interceptions but regrouped to make two scoring throws, culminating in the second TD to wideout Smith-Njigba in the extra period.
The Rams held a 13-7 lead at the break before Walker burst through for a 55-yard touchdown run for the home side.
Rams cornerback Wallace then took back Darnold's initial interception for a big return, leading to a one-yard touchdown by Blake Corum on the ensuing snap.
In the fourth quarter, a scoring pass from Matthew Stafford to Puka Nacua pushed the advantage to sixteen points, but Rashid Shaheed provided Seattle's hope with a 58-yard punt return.
Darnold then found AJ Barner in the end zone, and a converted two-point play forced the game into an extra period.
Although Nacua scored for his second touchdown in overtime, Jaxon Smith-Njigba answered in kind to set up the decisive score.
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