The 24 year old, nicknamed 'Spider-Man' because of his distinctive goal celebrations, has joined the Magpies from Spanish side Real Mallorca on a five-year deal for an undisclosed fee.
Keegan will hope Jonas' arrival is the first of several over the next few weeks as he attempts to drag the club back into the upper reaches of the Barclays Premier League table.
However, it is understood the right-sided midfielder's capture does not mean the Magpies are ready to re-think their decision to keep James Milner at St James' Park amid persistent links with both Liverpool and Aston Villa.
Keegan was delighted to have made the breakthrough after weeks of foraging by executive director (football) Dennis Wise and vice-president (player recruitment) Tony Jimenez.
He said: "Jonas is a wonderful signing for us.
"I know a lot of other clubs have been interested in him. He will be a terrific addition to the squad.
"He is an exciting player and I'm sure our fans will enjoy watching him."