Leicester was a "Scot and Lot" borough. All male ratepayers could vote.
Article about Leicester Parliamentary Borough at the time with list of elections, candidates & number of votes. Detail about elections in Leicester in 1760s.
"The History of Parliament - British Political, Social & Local History - Constituencies - Leicester"
https://www.historyofparliamentonline.org/volume/1754-1790/constituencies/leicesterPublished in "The History of Parliament: the House of Commons 1754-1790" editors L. Namier, J. Brooke, 1964
Right of Election: in the freemen and householders paying scot and lot
Number of electors: about 2,500
The right of election was confined to the corporation at one point in the 17th century (Corporation borough) and was later extended to freemen and scot & lot payers.
About a third of electors for Leicester Borough lived outside the borough but within the county.
1768 was the last contested election in Leicester until 1784. 2 candidates were eventually returned without an election in 1784. There were no elections 1769-1789. Next contested election was 1790.
https://www.historyofparliamentonline.org/volume/1790-1820/constituencies/leicesterNumber of voters: over 2,500
Population 16,953 (1801 census)
"City of Leicester Parliamentary History 1660-1835" in Victoria County History series, digitised as "British History Online"
https://www.british-history.ac.uk/vch/leics/vol4/pp110-152Very long article.
The franchise was vested in freemen and scot and lot payers from the first decade of 18th century. The corporation had limited the franchise prior to then.
A source for information in the article is "Historic Rights of Elections" by T. Carew (1755).