He previously served as the Mayoral Committee Member for Finance from 2006 until 2016 and Executive Councillor for Safety and Health from 2000 until 2002.

He has served as acting Mayor of Cape Town on two brief occasions in 2018, in May and from 31 October until Dan Plato was sworn in on 6 November.

He also worked on a number of flood and storm water projects, most notable of which was the design of the canal system at Century City in Cape Town, which later received an award from the Association of Consulting Engineers.

He was elected as a Proportional List Councillor to the Council of the Blaauwberg Municipality as the DP's sole representative.

[1] Soon before the 5 December 2000 local government election that established the new City of Cape Town, the DP amalgamated with the New National Party (NNP) to form the Democratic Alliance (DA).

[2] In October 2002 a number of former NNP members left the DA to reestablish their former party in the city council.

[7] The 2011 Local Government Election saw the Democratic Alliance returned to office with an improved vote share.

Councillor Johannes van der Merwe succeeded him as Mayoral Committee Member for Finance.

[11] Also, de Lille rejected an offer the Democratic Alliance to keep the position of Cape Town Mayor temporarily open while the parties discuss the matter in court.

On the same day, the Western Cape High Court ruled to reinstate de Lille as Mayor.

Neilson declared his candidacy for the post, but subsequently lost to former Cape Town Mayor, Dan Plato.