With a 15% swing against the sitting Liberal Democrats, Mr Hull took the Town Close ward with a majority of 193 votes.
A Green Party spokesman said:
'This magnificent by-election result will give our councillors the chance they need to press much harder to achieve Green goals such as more nutritious organic food for Norfolk schoolkids; more money across Norfolk for pedestrian-safety-schemes; and ethical investment for the county's own money.'
Green Party 1,151 votes (36%) Up 18% from last year
Liberal Democrats 958 votes (30%) Down 12% from last year
Labour 606 votes (19%) Down 1% from last year
Conservatives 470 votes (15% and 4th place) Down 5% from last year
The total electorate of Town Close is 7,811, and the turnout was 41%
The composition of Norfolk CC is now:
Lib Dem: 14