Meri Huws said 26 bodies must now meet Welsh language standards, making certain services available in Welsh.
The organisations involved include the Welsh Government, local councils and the three national parks.
The rules are intended to apply to further bodies in the future.
Some private firms are amongst the bodies that are due to come under the regulations at some point.
The regulations, which came into force on Wednesday, include requiring bodies to make it clear that they welcome correspondence with the public in Welsh and giving the language priority on bilingual signs.
They also give employees new rights to use Welsh in the workplace.
Speaking to BBC Radio Cymru's Post Cyntaf programme, Ms Huws said the changes were "exciting".
People should feel "confident" they can use services through the medium of Welsh at a number of public bodies, now new rules have come into effect, the Welsh language commissioner has said.