Maeda, who was part of Japan's squad at the recently concluded World Cup in North America, becomes Ipswich's first Japanese player. British media reported that the fee was about £10 million.
"I have always dreamed of playing in the Premier League, and I am very happy I can realise that dream with this club. I have loved all of the conversations with the club, and they have made me feel very welcome," Maeda said in a statement.
"My aim will always be to battle hard, score goals, and provide assists for my team - I will always run and give everything that I have."
The 28-year-old has scored five goals in 30 appearances for Japan, including in a 1-1 draw with Sweden in the World Cup group stage last month.
Maeda scored 79 goals in 212 appearances for Celtic, helping the Scottish champions to win five league titles and five domestic cups.
He joins Gary O'Neil's side ahead of the 2026/27 Premier League season as Ipswich's fifth signing of the close season. Ipswich begin their campaign against Sunderland on August 22nd.