Shares of the Akron, Ohio., company rose 2.37% to $34.15 in recent trading.
Icahn wants to narrow "the valuation gap between FirstEnergy and its peers," Bloomberg said.
FirstEnergy is navigating the after effects of a federal corruption case which saw the ouster of its CEO last October.
Icahn has a history of helping companies navigate through challenges. Icahn isn’t seeking control of the board, in part, because the utility sector is so heavily regulated when it comes to changes of control, Bloomberg reported.
On Monday, First Energy appointed Steven Strah its new permanent CEO. He had been serving as acting CEO since late October, after the company fired former CEO Charles Jones because he "violated certain FirstEnergy polices and its code of conduct."
Jones' firing came in the wake of guilty pleas by two people accused in a widespread corruption case against former Ohio House Speaker Larry Householder tied to a $1.3 billion bailout of two nuclear plants owned by a former FirstEnergy subsidiary.
Last month, First Energy officials in an annual investor call confirmed that they received a letter from Icahn Capital which said the company has a “present good faith intention” to buy $184 million to $920 million in voting shares.
In January, Icahn sold over half his stake in Herbalife Nutrition (HLF) - Get Report and relinquished his seats on the nutritional-supplements company’s board, taking a step back from a longtime investment he fiercely defended due to an onslaught from rival activist investor William Ackman, The Wall Street Journal reported.
(Updated to clarify that the nuclear plants are owned by a former FirstEnergy subsidiary.)