Packaging products maker Smurfit Kappa will join the benchmark FTSE 100 index later this month.
The Irish headquartered company is already quoted on the London 250 index as well as the Dublin stock exchange.
Also joining the FTSE 100 is medical products maker ConvaTec Group.
The two companies will replace precious metals mining company Polymetal International and Travis Perkins, Britain's biggest supplier of building materials.
Getting into the FTSE 100 can often fuel further demand for a company's shares, since funds that track the FTSE or invest in the index can then add that stock to their portfolio, while the inverse is true if a company falls out of the FTSE 100.
The rankings are decided on market capitalisation. Companies with the lowest market cap in the FTSE 100 drop into the FTSE 250 mid-cap index, and vice versa.
The changes will be implemented at the close of business Friday, December 16 and take effect on Monday, December 19.
Travis Perkins had warned in October that it would not meet market expectations for full-year profit, blaming a disappointing performance in its plumbing and heating business.
Polymetal, which pushed house-builder Berkeley Group Holdings out of the FTSE 100 index in August, has been pushed out of the index despite a surge in its share price as economic uncertainty had driven up the price of gold.
The company's share price had risen just over 30% so far this year.
