Question: Which of the following is grammatical?

> 
> * I am deputizing for him/her.
> * I am deputizing him/her.
> 
> 
> 

I think in the case of *covering* you have to use:

> 
> I am covering for him/her.
> 
> 
> 

...or do you?

Answer: 
[Merriam-Webster](http://www.merriam-webster.com/dictionary/deputize) shows a usage of *deputize* that somewhat agrees with your first sentence: *I deputize for the newspaper's editor on the weekends*. But it sounds strange to me. I'd say that I was *acting for* or *covering for* someone not available to do the work at the moment, or that I had been authorized to act as that person's *agent*. I associate *deputy* with legal positions, like deputy sheriff and deputy district attorney. There may be a distinction in British and American English, though.

*I am deputizing him/her* means that you are authorizing someone else to act as a deputy.
I think both are correct but each has a different meaning:

**1-** I am **deputizing for** him/her. (*intransitive*)

**2-** I am **deputizing him/her**. (*transitive*)

The verb '**deputize**' is both transitive and intransitive. 

**1-** In the transitive form (*second* example), the verb **deputize** would mean **appoint**, and must be followed by an object that would serve as the **appointee**. So, the sentence would mean: 

**I am deputizing** (= appointing) **him/her**.

In the passive:

**He/She is being deputized (= appointed) by me.**

**2-** When **deputize** is followed by preposition **for** (as in the *first* example), it would mean **replace, substitute, or stand in for**; the object after **for** denotes the **substituted**, and the subject denotes the **substitute**:

**I am deputizing for** (= I am replacing, or standing in for) **him/her**.

**3-** When not followed by an object or preposition **for**, **deputize** would still be intransitive and mean **replace.** Here's an example (from Longman dictionary: <https://www.ldoceonline.com/dictionary/deputize>):

**My boss had to go to the Caribbean unexpectedly and asked me to deputize.** (That is, my boss asked me to replace someone)