The council already had approved the smoking ban earlier in the month, but because of a technical issue, it required a third reading.
The council members, including Macon Cowles, who was absent at the previous meeting, voted unanimously to support the smoking ban.
They said they may ban smoking in all public places, including parks, in the future.
The ordinance goes into effect in 30 days, but city officials have said they anticipate a "soft" transition, with officers first issuing warnings. They likely will start writing tickets sometime in March.
The ordinance bans all smoking -- whether tobacco or marijuana -- on the four blocks of the Pearl Street Mall and on the lawn of the Boulder County Courthouse.
A first or second offense within two years would result in a ticket up to $500.
A third offense in two years could result in a fine of up to $1,000 and up to 90 days in jail.