The investment trusts run by City veteran Neil Woodford and Terry Smith will be promoted to the FTSE 250 index on Christmas Eve.
The latest reshuffle of the midcap index will see Woodford Patient Capital, which invests in early stage growth companies, join the flagship index after it was boosted by rising valuations of several of its holdings.
The shares of the £977m trust have risen from 74p to 87p over the past six months.
The promotion is likely to boost the share price, as many passive investment funds which buy either the FTSE All Share index or the FTSE 250 Index, would be required to buy the shares of the trust, ensuring a more constant level of demand.
In performance terms the trust has enjoyed a strong twelve months, returning 5 per cent, compared with a loss of 2 per cent for the average trust in the AIC UK All Companies sector over the past year.
Laith Khalaf, senior analyst at Hargreaves Lansdown said: "Strong share price appreciation from companies like Autolus, Benevolent AI and Proton Partners has helped repair the damage from failed clinical trials at Prothena in April, and Woodford Patient Capital Trust is now trading at close to its highest level so far this year.
"The nature of the early stage businesses this trust invests in means performance can be expected to be volatile and lumpy, and so the fund is suited to investors who are adventurous and patient, as the name suggests."
The Smithson Investment trust, a company for which Terry Smith of Fundsmith acts as chief investment officer, broke Mr Woodford’s record for largest investment trust launch when it raised £882m via an Initial Public Offering (IPO) in October.
The trust trades at a premium to net assets of 5.5 per cent, according to data from the Association of Investment Companies (AIC).
Trusts trading at a steep premium to net assets can be off-putting to investors as they are effectively paying more for the assets held in the trust than the value of those assets on the open market that day.
But the shares having a constant buyer via the passive investment funds will make it more likely that the premium will persist.