Town have confirmed that Alan Judge has signed his new contract, which as previously reported runs to the summer of 2021 with the deal having an option for a further year.
"It’s great news for the club that we have Judgey signed up,” boss Paul Lambert told the club site. "The supporters have taken to him and his quality is clear to see.
"I know he wants to play for Ireland as well so playing games regularly here can only help in that respect.”
The 30-year-old joined the Blues on a short-term contract in January for a nominal fee from Brentford.
That deal included an option for a further season, however, discussions regarding a longer extension have been ongoing for a number of weeks.
Since signing, the Republic of Ireland international has become a key player as Lambert has sought to instil his passing style in his team and confirmation that the Dubliner will be at Portman Road will be a big boost for supporters ahead of what will almost certainly be a 2019/20 campaign in League One.