Preston County, Virginia voters elected McGrew and Congressman William Gay Brown, Sr. as their delegates to the Virginia Secession Convention in 1861, where both were Unconditional Unionists and voted against secession on both April 4 (when the ordinance was defeated) and April 17 (when it passed). The Wheeling Convention was held on May 13–15, led by Preston County's William B. Zinn. On June 29, 1861, after Virginia voters approved secession, other delegates expelled them from the convention, and replaced them with secessionist Preston County lawyers Robert E. Cowen and Charles J. P. Cresap.