Donegal are almost certain of promotion while Louth have been relegated from Division 2 of the Allianz Football League following their 1-19 to 3-07 defeat in Ballyshannon.
Jim McGuinness' side led 0-13 to 1-01 at half-time, with Shane Lennon toe-poking home Louth's 34th-minute goal.
Goals from Paddy Keenan and Brian White reduced the deficit to three points, but David Walsh's late goal capped off the win for Donegal who barely had to get out of second gear.
There was some surprise that Donegal started Paddy McBrearty and brought on Ryan McHugh at half-time with both players involved in next Wednesday's Ulster U-21 semi-final against Armagh.
Donegal were totally dominant in the middle third in the first half with Christy Toye and Rory Kavanagh scoring four points between them before the break.
Louth lost two players to black cards and took their time to adjust. Full-back Dessie Finnegan was forced off in the fourth minute and full-forward Eoin O'Connor joined him in the 30th minute for hauling down Colm McFadden.
Dermot Molloy, playing on the forty, scored 0-02 from play in the opening half with wing back Anthony Thompson also on the scoresheet as Donegal raced clear.
Louth midfielders Paddy Keenan and Brian Donnelly were much improved in the second half, as they looked to spearhead a revival from the Wee County.
Toye's third point, a Michael Murphy free and a Colm McFadden point extended Donegal's lead to 0-16 to 1-2 after 47 minutes. But Louth then enjoyed their best spell of the game, registering an unanswered 2-02 in the space of five minutes.
A brace of points from Brian White was followed by two goals in a minute from Keenan and White, who both drove straight through the middle of the Donegal defence to drill goals past net minder Paul Durcan.
With their cushion cut to three points, substitute David Walsh settled any Donegal nerves with a goal after 56 minutes.
Louth have seemed doomed to relegation from early in the campaign and never looked like salvaging anything from this trip to the north west.
Shane Lennon (free) and Evan Duffy scores did reduce the deficit to four points again, before Murphy scored his only point from play to complete a convincing win for Donegal, which virtually assures instant promotion for them back to the league's top tier.
DONEGAL: P Durcan; E McGee, N McGee, K Lacey; Declan Walsh (0-01), L McLoone, A Thompson (0-01); R Kavanagh (0-02), C Toye (0-03); M McHugh, D Molloy (0-02), O McNelis; C McFadden (0-06, 0-03f), Michael Murphy (0-04, 0-03f), P McBrearty.
Subs: R McHugh for Lacey (half-time), David Walsh (1-00) for McBrearty (55 mins), L Keaney for Thompson, G McFadden for Kavanagh (both 69).
LOUTH: N Gallagher; P Rath, D Finnegan, J O'Brien; G O'Hare, D Crilly, A Reid; P Keenan (1-00), B Donnelly; P Reilly, B White (1-03, 0-01f), S Campbell; A McDonnell, E O'Connor, S Lennon (1-03, 0-02f).
Subs: D O'Hanlon for Finnegan (black card, 4 mins), C Judge for Campbell (21), E Duffy (0-01) for O'Connor (black card, 30), D Brown for Judge (32), D Clarke for Donnelly (63), L Shevlin for Reilly (65).
Referee: Martin Higgins (Fermanagh)