The local authority owns the tower at the 19th Century criminal and civil courts complex.
A new viewing platform has been created on the tower.
The rest of the castle is to be turned into a visitor centre once new a courts building is constructed on another site in Inverness.
Highland Council, Inverness Common Good Fund and Highlands and Islands Enterprise have all contributed to the cost of the North Tower project, which includes new access, a shop and a stairway to the roof and viewing platform.
Inverness City Region Deal money has also been made available to improve the approaches to the 175-year-old North Tower and castle, which will include an upgrade of Castle Wynd.
Inverness Provost Helen Carmichael said: "The views are spectacular from the top and I am confident that visitors to Inverness will be delighted with the Castle Viewpoint.
"It adds significantly to the city's draw as a worldwide tourist destination."
Highland Council's leader, Margaret Davidson added: "I am delighted that the Castle Viewpoint will be open for Easter.
"The first week will be free to visitors and locals who wish to get a look at how the tower has been transformed."
The North Tower of historic Inverness Castle is to be opened as a tourist attraction by Easter, Highland Council has said.