RHS director general Sue Biggs and HTA chief executive Carol Paris will speak at the event and Defra minister George Eustice is set to back the roundtable's 12 action points.
Paris will speak on skills and careers and has been focussing on the commercial side of the plan.
Martin Emmett has been addressing education and employment, while Alastair Griffiths has been looking at science and research development.
Paris said she hopes Eustice will promote the plan positively and successfully to the large number of Parliamentarians expected to attend.
The RHS said: "The event is a great high profile opportunity to continue promoting these themes to an influential audience."
Plans to fix the supply chain include developing a best-practice hub as a resource for suppliers, encouraging fairness and transparency to promote competitive trading.
Government-focused "asks" from the 12-point plan include the creation of a year-long international garden expo, provision of higher-level horticultural apprenticeships, increased use of horticulture in the curriculum, and more research and development funding.