He sat in the front row at the announcement alongside National MPs Simeon Brown and Kanwaljit Singh Bakshi, Health Minister David Clark and Pacific Peoples Minister Sua William Sio.
Before announcing the new mental health unit, Clark noted Ross' presence, saying: "I'd like to pay particular respect and honour today to fellow MP and Botany MP Jami-Lee Ross. It is really good to have you here today."
Ross later said he did not want to talk politics at the event.
"[Middlemore] did a fantastic job and they're just amazing people and this is their special day.
"So I just wanted to be here to support them.
"I'm not here to talk politics, I'm here as a local MP, but also as someone that is thankful for everything."
In October, Ross was taken into care at Middlemore's mental health unit for two days.
His appearance today comes after a turbulent few weeks for the MP.
In early October, National Leader Simon Bridges said Ross would be absent from Parliament for a few months while he dealt with personal health issues.
A few weeks later, Bridges said the PwC investigation into the leak of National Party travel expenses concluded that on the "balance of probabilities the evidence establishes that Ross was the person who leaked the expenses and the sender of the text message".
The next day, in an hour-long media stand up, Ross launched a scathing attack on Bridges over claims of electoral fraud – claims that Bridges denied – Ross resigned as a National MP, but said he would stay on as the local MP for Botany.
He then proceeded to leak secretly record phone conversations between himself and Bridges to media.
Ross was taken into care at the mental health unit of Middlemore later that week.
He has not made a public appearance since he was discharged on October 23.
