Bannigan and Thistle team-mate Stephen O'Donnell have both been included in Billy Stark's squad for Wednesday's friendly against Greece in Korinthos.
The pair caught the eye of Stark after an impressive run of results by the First Division side, and Bannigan acknowledged McNamara's role in their success.
The midfielder said: "He was the one who played us every week and got Thistle playing some not bad football.
"It's mostly down to him, although the players on the park are doing it as well."
The phone call that broke the news of the call-up came from McNamara, who quit Firhill to take over at Dundee United last week.
Bannigan added: "It was unexpected. I got a phonecall last Sunday night just saying it was a possibility and to be aware of it.
"I wasn't taking it for granted until it was official. I then found out for certain on the Monday.
"It was a good feeling. I've never had this before at any level.
"There is a wee bit of apprehension but I'm just delighted and looking forward to it.
"I'm a First Division player but they obviously recognise we are doing not a bad job at Partick Thistle."
With the qualifiers for the UEFA European Under-21 Championship for 2015 set to get underway next month, Bannigan is determined to seize his opportunity to impress Stark.
He said: "I'll just come in and play the way I usually do. I won't try anything different.
"Hopefully I get a bit of game-time on Wednesday and show what I can do.
"I don't know much about the opposition yet but it's something I'll just have to adapt to.
"I've not really played any European football so this will be my first taste of it.
"If you want to be the best in football, you have to play against different kinds of players. I'm sure we will do fine."
The young Scots will face the Netherlands, Slovakia, Georgia and Luxembourg in the qualifiers but Bannigan refused to look too far ahead.
He added: "I'll just concentrate on this week and see how I do and, if I do well, hopefully I'll get the call-up for the next games."
Meanwhile, the 20-year-old remains confident of success for Partick this season under the interim leadership of Alan Archibald, despite the departure of McNamara.
He said: "Big Archie has come in and brought in Scott Paterson as his assistant so I'm enjoying working with them just now.
"I had a couple of days with them last week and nothing has really changed. We've still got the same group of players.
"We are obviously a wee bit disappointed about Jackie leaving but that happens in football.
"We've got a couple of games in hand over Morton and, if we win those games, we can still go top so I'm very confident."