The South Yorkshire club had been well-positioned to cause an upset when winger Ollie Greensmith scored a try with the final play of the first half at Derwent Park.
Matty Beharrell converted from the touchline to leave Doncaster just 18-12 behind against opponents who were favourites to follow fellow Cumbrians Barrow Raiders into the second tier.
However, Richard Horne’s side were too error strewn in the second period, making countless errors, and it was no surprise their hosts duly picked them off.
Doncaster finished fifth and won three successive play-offs to get to this decider but Workington, who came second in the table, always had that little bit of extra class and composure.
The Dons, who had beaten Workington in both their previous meetings this term, knew they could not start slowly having come from 12-0 behind to sneak past Keighley Cougars in the final minute the previous week.
However, Horne’s side did just that after a midfield break from stand-off Jamie Doran gave position for Joe Brown to score within just two minutes.
Carl Forber slotted the first of his six goals but Town - coached by ex-Huddersfield Giants assistant Chris Thorman - then saw Declan O’Donnell sin-binned for a late shot on Beharrell.
Doncaster managed to build some pressure of their own for Liam Johnson to go over from Jake Sweeting’s pass, Beharrell kicking the first of his two goals.
But, in rampaging prop Connor Fitzsimmons, Workington boasted the man-of-the-match and he barged over just before O’Donnell returned to the field.
It was also Fitzsimmons who slipped Forber over between the posts in the 33rd minute to stretch the lead further.
On-loan Wakefield Trinity winger Greensmith clawed Doncaster back into it and, though they competed hard in the second half, once Matty Henson followed up his own kick to score in the 50th minute, it was always going to be tough to recover.
Workington scored two tries late on via Marcus O’Brien and Brad Holroyd to add some gloss before their ecstatic fans surged onto the field to join in their celebrations.
Workington Town: Holroyd; Young, Brown, Bickerdike, Olstrom; Doran, Forber; Lightowler, O’Donnell, O’Brien, Fitzsimmons, Barnes, Dawson. Substitutes: Henson, Clarke, Singleton, Wilson.
Doncaster RLFC: Taulapapa; Halliday, Smeaton, Tali, Greensmith; Sweeting, Beharrell; Braham, Cockayne, Douglas, Johnson, Ollett, Foster. Substitutes: Holdstock, Johnston, Whitmore, York.
Referee: Tom Grant (Leeds)