There are other contenders. But here in Duck Soup (1927), Stan Laurel and Oliver Hardy are teamed up as co-stars for the duration of the two reels.
In this film, whose title would be re-used some years later by Leo McCarey for the Marx Brothers’ masterpiece, Laurel and Hardy play two down and outs. It turns out that local rangers have acquired somewhat fascistic powers to pick up anybody who doesn’t look like they have roof over their head, and compel them to fight dangerous forest fires.
A ferocious old big game hunter is meanwhile off to decimate some wildlife somewhere and the staff of his mansion take the opportunity to take a holiday of their own. Stan and Ollie end up crashing the unoccupied establishment (following a terrifying downhill bicycle ride to escape the rangers) but then have to impersonate the proprietor and the maid in an attempt to rent the place to some visiting toffs. Eventually, Stan’s skirt is snagged on a nail, exposing his breeches beneath and revealing the subterfuge to the head ranger who forces them both to wield a dangerous and out of control firehose while attempting to check a deadly conflagration. The end. The idea was taken from a music hall routine written by Stan’s father, Arthur J. Jefferson, and the substance of the plot would be recycled by Laurel and Hardy for their sound comedy “Another Fine Mess”.
An unshaven Ollie sports a battered top hat and monocle as his hobo costume while a rather youthful and good looking Stan wears a slightly larger bowler hat than we subsequently become used to seeing him wearing… one that actually fits him and makes him look rather dapper.
The real puzzle is why it took a while for these two to become an established partnership after this was made. This is not presented as a Laurel and Hardy film, just a film in which Laurel and Hardy happened to co-star.
There are double acts which consist of two funny people working together and double acts which consist of people who are funny BECAUSE they are together. Laurel and Hardy are the latter, but not quite yet, not quite in this film. Once in the house, they separate. Although they are co-leads in this effort, they don’t yet spend enough time just reacting to one another, emotionally as well as physically.