Ilves divorced his second wife Evelin in April.
"Toomas Hendrik Ilves and Ieva Kupce got engaged in the middle of November. It is their personal decision and is not connected to the official duties of Ilves as the head of state," a spokesman for the president Toomas Sildam told the Estonian daily Postimees.
Kupce is the head of the Latvian Defense Ministry's national cyber security policy coordination section.
She began her diplomatic career in the Ministry of Foreign Affairs in 1997 and continued her work in the field of foreign and security policy in different institutions focusing on the issues of security, democracy, and human rights.
The couple have been seen together frequently in recent months.