McGilvra served one term in the Territorial Legislature of 1866-67, and during the session procured an appropriation of US$2,500 for a wagon road across the Cascade Mountains through the Snoqualmie Pass. This amount was supplemented by an appropriation of like amount from King County and by later appropriations and contributions the road was kept open, and for many years was the only means of communication across the Cascade Mountains north of the Columbia River.