Billy Sharp's second-half double confirmed Scunthorpe's promotion to the second tier of English football for the first time in 44 years.
United's striker had an early half volley tipped over by Town keeper Matt Glennon in a nervy opening 45 minutes.
But Sharp prodded in his 27th league goal of the season when Glennon parried Kevan Hurst's shot into his path.
And Iron fans were spared a nail-biting climax to the game when Joe Skarz handled in the box and Sharp converted.
Scunthorpe: Murphy, Byrne, Foster, Butler, Williams, Taylor (Sparrow 57), Goodwin (Baraclough 76), MacKenzie (Hinds 88), Hurst, Beckford, Sharp.
Subs Not Used: Lillis, Quinn. Booked: Goodwin.
Goals: Sharp 68, 84 pen.
Huddersfield: Glennon, Collins, Sinclair, Mirfin, Skarz, Hudson, Worthington, Ahmed, Booth, McAliskey (Racchi 73), Beckett.
Subs Not Used: Eastwood, McIntosh, Berrett, Hand.
Scunthorpe are promoted
Ref: E Ilderton (Tyne & Wear).