Sadiq began his political career as a member of the Pakistan Tehreek-e-Insaf in the late 1990s when he was a close friend of PTI chairman Imran Khan. Sadiq ran for the seat of Provincial Assembly of the Punjab as a candidate of PTI in 1997 Pakistani general election from Constituency PP-121 Lahore but was unsuccessful. He received 4,541 votes and lost the seat to Pakistan Muslim League . Sadiq left PTI in 1998 owing to differences with Imran Khan and joined PML in 2001. Sadiq was elected to the National Assembly of Pakistan as a candidate of PML-N from Constituency NA-122 on 2002 general election, by defeating Imran Khan. Sadiq claimed "it was a big victory as his leader Nawaz Sharif in exile and Pervez Musharraf, a close aide of Imran Khan at that time, in power". During his tenure as the member of the National Assembly, he remained a member of the National Assembly's Standing Committees on Railways, Finance and Defence Production. Sadiq was re-elected to the National Assembly as a candidate of PML-N from Constituency NA-122 in 2008 general election. During his tenure as the member of the National Assembly, he became the chairman of the National Assembly's Standing Committees on Railways. Sadiq was re-elected to the National Assembly as a candidate of PML-N from Constituency NA-122 in 2013 Pakistani general election, by defeating Imran Khan. In June 2013, Sadiq was elected as the Speaker of the National Assembly of Pakistan. In 2015, Imran Khan alleged rigging in the constituency of Sadiq from where Sadiq won in 2013 election. Following which the Election Commission of Pakistan de-seated Sadiq and ordered re-polling in the constituency. In October 2015, Sadiq retained his National Assembly seat by defeating a PTI candidate in by-election and was re-elected to the National Assembly for the fourth time. In November 2015, Sadiq retained its position as the speaker of the National Assembly by getting re-elected for the second time and become first person to have been elected as the Speaker of National Assembly for the second time during the same government's tenure in Pakistan. He was re-elected to the National Assembly as a candidate of PML-N from Constituency NA-129 in 2018 Pakistani general election. On 15 August 2018, he was replaced by Asad Qaiser as speaker of the National Assembly. He is generally considered a soft-spoken and cool-headed politician in Pakistan.