Sinnott replaces Dave Frecklington, who was sacked last week with Trinity currently third-bottom of the table.
Sinnott was a vastly experienced player with over 500 Football League appearances with the likes of Walsall, Watford, Bradford City, Crystal Palace, Bradford City and Huddersfield Town and has since had over fifteen years in management with the likes of Farsley Celtic, Port Vale, Bradford Park Avenue and Altrincham,
The 52-year-old will oversee training this evening and admitted: "Gainsborough has always had a great deal of potential when I have visited with other clubs, but the hard work starts now, and I can't wait to turn that potential into reality."