The Parliament was originally suggested by the last Supreme Dalek of the Daleks, who was defeated many times by the Doctor and he eventually, like Dalek Sec before him, realised that the Daleks were not the Supreme Beings after all, and ended their 3-millenia conquest to destroy all life.
As a Democratic organization, The Parliament is ruled over by a Prime Minister, who takes the opinions of all the Daleks into account. He also dispatches battlegroups of Daleks (led by the Blue Dalek General) to aid the League where necessary.
There are drawbacks to the Parliament though, most notably the failures that call themselves the Dalek Rangers. Also, the Parliament fought a war with the Cybermen and lost pitifully, which stained their record as the 'Supreme Beings'.
The creation of the Parliament has ended the Dalek's reign of tyranny and made them an accepted member of society. They even helped to defend the Humans in the Third Galactic War, and have helped the League in many other wars before and since. Historians revel at the day that the Daleks finally become an accepted species in league society. Lets hope it lasts.