[3] Sanderson first became Member of Parliament (MP) for Colchester at a by-election in 1829—held due to the resignation of Sir George Smyth, 6th Baronet.
At a dinner in July of the same year, he lamented that "nothing of great importance" had taken place in the House, but he was prepared to "stand forward in support of those principles which he had publicly avowed".
[3] As the 1830 general election approached, Sanderson sought to retain the seat but was forced to pull out at a late stage when his agent was spotted in an act of bribery.
At the general election a year later, he again sought to represent the seat, gaining corporation backing, in a bid to prevent the return of reformers.
Nevertheless, he attended the hustings, promising to accept "the necessity of parliamentary reform", an extension of the franchise to "large and populous places", but still rejected the need to disenfranchise other seats.