If a single man marries his girlfriend will he pay less in taxes?

Yes because your exemption credits will double & your standard deduction will too..

If you file single in 2014 -- the first $10,150 is tax free for federal. If MFJ -- you don't pay any taxes on the first $20,300 (you said your gf had zero income)

If you are filing a joint return & shes a student & has qualified tuition & receives a 1098 T; the 2 of you may qualify for an ed credit also..

You may also be able to take a deduction for student loan interest..

in USA, yes but that is an expensive way to save pennies.

visit a library for books on doing taxes.

she may have student problems with tuitions.

he doesn't claim her as a dependent, she is a co taxpayer with him

he files a joint return with her and now that he is married he has a different amount for his standard deduction, he also adds one more personal exemption to reduce his taxable income

as a student there could possibly be a credit that can be claimed as well

Yes, if she has no income and they file jointly, he will pay less.

Yes, if he's paying any tax.

Maybe

Some yes.

When couples with unequal income wed, their joint taxes almost always go down significantly.