Greece's radical new leftist government wants an old conservative to be the country's president
Pavlopoulos was a minister under New Democracy between 2004 and 2009.
That might seem like an odd choice, but it makes sense in the same way that far-left Syriza's coalition with the right-wing Independent Greeks makes sense. Tsipras wants to concentrate on ending Greece's bailout and doesn't want any distractions.
So if supporting a centre-right candidate for the presidency puts one less thing on his plate (since conservative lawmakers will vote with him, not against him) it's a good idea.
The presidential elections are coming round because the previous Greek government failed to get its candidate elected, which actually sparked the whole general election that let Syriza into power in the first place. Tsipras, understandably, doesn't want anything like that to happen to him.
Though this time, the parliament will be able to appoint a president with a simple majority (151) of Greece's 300 MPs. Previously, 180 votes were needed.