Harps had started the brighter, but were wasteful with a number of moves down the flanks and didn't cause Robbie Horgan as much trouble as they probably could have.
In the first half, player-manager Gorman went close with a 25-yard strike but he watched his effort rebound off the post, while he had an earlier free-kick which was easily collected by Horgan.
David Lee had Monaghan's only noteworthy opening of the first half but he shot wide of James Gallagher's goal from 18yards, but at this stage Harps really should have been in front after Barry Curran missed the best chance of the opening 45.
Matthew Crossan played a delightful ball in over the top for Curran, who beat the offside trap, but miscued and shot wide of goal when it seemed easier to score or centre for one of his comrades in the middle.
The second half began in a rather lacklustre manner with chances again restricted to the long-range efforts, but the only goal of the game did arrive 21minutes into the second period to leave the large band of vocal Harps fans in fine tune.
Six minutes after the hour mark, Harps grabbed the lead goal when ace-marksman Walsh beat Robbie Horgan with a neat right-footed effort from the edge of the box after Matthew Crossan and Stephen O'Donnell both had balls in blocked down by the home defence.
Thereafter, chances were in limited availability and Harps were happy to hold onto their advantage with Monaghan posing little or nothing in the way of a threat on James Gallagher's goal.
The win keeps alive the Donegal men's hopes of a fourth placed finish although they will be tested in their final four games with three of the top four still to be faced.
Harps now host Limerick FC, who occupies the place above them in the table, at Finn Park next Saturday night next.
Monaghan United: Robbie Horgan; Brian Gannon, Michael Kerr, Paul Whelan, Darren Sargent; David Lee, Austin McCann, Jimmy Fullam, Paul Smith; Cian Mackey, Robbie Smith. Subs: Stephen Finnegan (for Fullam, 70mins); Tommy Toal (for Sargent, 72mins); Finbar Heffernan (for Mackey, 80mins).
Finn Harps: James Gallagher; Sean McGowan, Jonathan Minnock, Eloka Asokhu, Shane Bradley; Michael Funston, Matthew Crossan, Barry Curran, Anthony Gorman; Stephen O'Donnell, Davitt Walsh. Subs: David Bell (for Minnock, h/t); Darren Meenan (for Curran, 71mins).
Referee: Damien Hancock
Finn Harps Dot Com Man-of-the-Match: Davitt Walsh made a scoring return to the Harps line up with the Kerrykeel native's second half goal proving to be the match-winner.
Walsh's overall contribution was excellent with his work rate and link up play excellent and he grabs the Man-of-the-Match award for this top-class performance.