In 1832, the Surveyor-General at the time, Sir Thomas Mitchell, commissioned Lennox for a sum of £1083 to build a bridge at the intersection of Prospect Creek and Southern Street, which would be named "Bowler's Bridge" after Lansdowne's local innkeeper. The sandstone used in designing the bridge was found in a quarry only 11km from the proposed site of the bridge, allowing workers to row a punt to transport the stone to the construction site. On January 1, 1834, the foundation stone was laid. The bridge was constructed entirely by unskilled Australian convicts, despite Lennox's numerous requests to Mitchell for skilled labourers. The bridge was completed a year later in 1835, and opened on January 26, 1836, the 48th anniversary of the Colony of New South Wales, before a crowd of around 1,000. Later, Richard Bourke, the Governor of New South Wales, wrote that the bridge had cost only £1000 to build, compared to the £7000 it would have taken to build a bridge of the same quality in England.
In 1973, Australia recognized Lansdowne Bridge for being "one of the finest examples of Colonial Architecture in Australia". In 1990, the Environmental Management Committee Fairfield Council confirmed that Lansdowne Bridge had the largest span of all masonry bridges in Australia and in 1992 that it was an example of excellent construction, which should be preserved. Lansdowne Bridge is also listed on the Register of the National Estate and on the National Historic Engineering Landmark list.
- "Lansdowne Bridge over Prospect Creek". New South Wales Department of Roads and Maritime. 7 July 2014. http://www.rms.nsw.gov.au/cgi-bin/index.cgi?action=heritage.show&id=4301042. Retrieved 3 November 2015.
- "Lansdowne Bridge". Heritage Council of New South Wales. http://www.environment.nsw.gov.au/heritageapp/visit/ViewAttractionDetail.aspx?ID=5051374#. Retrieved 3 November 2015.
- "Lennox's Lansdowne Bridge". The Institution of Engineers Australia. March 1986. https://www.engineersaustralia.org.au/portal/system/files/engineering-heritage-australia/nomination-title/Lennoxs_Lansdowne_Bridge_Nomination.pdf.
- "Historical Archaeological Sites – Lansdowne Bridge". Fairfield City Council. 15 July 1992. http://www.fairfieldcity.nsw.gov.au/upload/uwshv69639/Hume_Hwy_No45_Lansdowne_Bridge.pdf.
- Australian Heritage Commission (1981). The Heritage of Australia. p. 2/24. ISBN 0333337506.