The top-seeded Seahawks, who were 13-3 in the regular season, justified their ranking with an overpowering first half in taking a 16-0 lead before holding off a second-half surge by the battling Saints.
Lynch ran for 140 yards and two touchdowns, including a 31-yard romp that padded Seattle's lead to 23-8 with 2:48 left.
New Orleans moved within one last desperate chance after quarterback Drew Brees hit Marques Colston with a nine-yard touchdown pass to make it 23-15 with 26 seconds to play.
The Saints recovered the onside kick and had two completions before Colston tried to extend the play with a forward lateral and the infraction resulted in a 10-second run-off that ended the game.
The Seahawks, who have won 16 of their last 17 home games, will next host either the Carolina Panthers or San Francisco 49ers next Sunday for the NFC championship and a berth in the Super Bowl next month in New Jersey.
Seattle stifled the Saints' passing attack in the first half, holding Brees to 34 yards through the air as he completed 5-of-12 throws.
Lynch scored on a 15-yard burst up the middle and Steven Hauschka kicked field goals from 38, 49 and 26 yards for a sizeable cushion at the intermission.
New Orleans dominated the action in the second half.
Khiry Robinson dove in from the one-yard line early in the fourth quarter to make it 16-8 and with the Saints' defense holding down the Seahawks' attack, Brees brought New Orleans within range of tying the score.
The Saints marched to the Seattle 25-yard line, needing a touchdown and two-point conversion to tie.
But Seattle pushed them back and Shayne Graham missed a 48-yard field goal try, his second miss of the game.
Seattle secured their lead when quarterback Russell Wilson converted a third-and-three on a twisting, sprawling catch by Doug Baldwin one play before Lynch bounced outside and rambled into the end zone from 31 yards out.
Brees finished with 309 yards passing, hitting 24 of 43 passes against the fierce Seattle secondary. Wilson, relying on the running of Lynch, completed 9 of 18 for 103 yards through the air.