Cum­mings was one of the or­ga­ni­zers of the Bos­ton So­ciety of Ar­chi­tects in 1867, its vice-president in 1885 and 1886 and from 1887 to 1896, and its pre­si­dent from 1896 to 1901. He was elec­ted an As­so­ciate of the Ame­ri­can In­sti­tute of Ar­chi­tects in 1870 and a Fel­low in 1889. He ser­ved on many pu­blic com­mit­tees on the com­mis­sion for pre­ser­ving and res­to­ring the Mas­sa­chu­setts State House and later on the City's Art Com­mis­sion. He was pre­si­dent of the Per­ma­nent Com­mit­tee of the School at the Mu­seum of Fine Arts and a trus­tee of the Bos­ton Athen­aeun and of the Mu­seum of Fine Arts.