Learn Hardcore Chinese: tā zài zhè gè chéngshì zhù le sān nián le. - He has lived in this city for three years.

The first 了, after 住 → 住了, is the aspect particle. It marks the action as having occurred / been completed up to some point. With a duration phrase, it helps form the idea “has (already) lived for …”.
The second 了, at the end of the sentence, is the sentence-final 了. Here it shows a change of state or a new situation: “Now, as things stand, he has lived here for three years.”

Together, 住了三年了 expresses:

the action has lasted three years, and
this situation is true now and still continuing (he is still living there).

Does this sentence mean he is still living in this city, or that he has already left?

It means he is still living in this city.

Pattern: [verb] + 了 + duration + 了 (here: 住了三年了) usually means:

The action started in the past,
It has lasted for that duration, and
It is still ongoing now.

So 他在这个城市住了三年了 is best understood as:

He has been living in this city for three years (and he still lives here).

What would change if I remove the final 了 and just say: 他在这个城市住了三年?

他在这个城市住了三年 is grammatical, but the nuance is different:

他在这个城市住了三年
Often implies a completed period in the past. It can easily be understood as “He lived in this city for three years (but not anymore).” Context decides, but the “finished period” reading is common.
他在这个城市住了三年了
Strongly suggests “up until now, it has been three years, and it’s still true.”

So, adding the final 了 tends to emphasize that the situation continues into the present.

Why is it 在这个城市住 and not 住在这个城市? Are both correct?

Both are correct; the difference is mainly in word order / emphasis, not meaning:

他在这个城市住了三年了。
Literally: He, *in this city, has lived three years (now).*
- 在这个城市 is a location phrase placed before the verb.
- This is very natural and common in Chinese: 在 + place + V.
他住在这个城市三年了。
Literally: He has lived *in this city three years (now).*
- Here 住在 is treated as a verb + preposition chunk, “live in”.

Both mean essentially the same thing: He has lived in this city for three years (and still does).

In practice, 在 + place + 住 (the original sentence) is slightly more common in speech, but 住在 + place is also very natural.

What does 在 (zài) mean here? Is it the same 在 as in the progressive form like 我在吃饭?

Yes, it’s the same character 在, but used in a different way:

In 他在这个城市住了三年了, 在 is a preposition / coverb meaning “in / at”, introducing a location:
- 在这个城市 = in this city.
In sentences like 我在吃饭, 在 functions more as a progressive marker (“be doing”) plus sometimes a locative sense, depending on context.

Grammatically, Chinese grammars often group these uses together under 在 + place / action, but in this sentence the main role is to mark the place where he lives. It does not directly mark progressive aspect here; that role is mainly played by the 了…了 structure.

Why do we need the measure word 个 (gè) in 这个城市? Why not just say 这城市?

In Chinese, when you use a demonstrative (like 这 = this) before a countable noun, you normally need a measure word in between:

这 + 个 + 城市 = this + [generic classifier] + city.

个 is the most common, general-purpose measure word. So:

这个城市 = this city (correct and natural)
这城市 is possible in some informal or literary styles, but:
- It sounds more colloquial / non-standard in everyday Mandarin.
- For learners, always using 这 + 个 + noun is safer and more standard.

So 这个城市 is the normal, standard phrase you should learn.

How do I know that 三年 here means “for three years” and not “three years ago”?

Because of the structure and position of 三年:

In 他在这个城市住了三年了, 三年 follows a verb + 了 and functions as a duration:
- 住了三年 = lived for three years.

To say “three years ago”, Chinese normally uses 三年以前 / 三年前, and the time expression goes before the verb:

他三年前在这个城市住过。
He lived in this city three years ago.

So:

住了三年 → duration: for three years
三年前 / 三年以前 → point in time: three years ago

Can I add 已经 (yǐjīng, already) to this sentence? Where would it go, and does it change the meaning?

Yes, you can add 已经, usually before the verb or before the location phrase:

他已经在这个城市住了三年了。
他在这个城市已经住了三年了。

Both are natural.

Meaning-wise:

Without 已经: 他在这个城市住了三年了。
= He has lived in this city for three years (now).
With 已经: emphasizes “already”:
他已经在这个城市住了三年了。
= He has already lived in this city for three years.

The core meaning (he’s been living there for three years and still lives there) is the same; 已经 just adds emphasis.

Why can’t I say 他住了在这个城市三年了?

他住了在这个城市三年了 is ungrammatical because the order of 住, 了, 在这个城市 is wrong.

Key rules:

在 + place must go directly before the main verb (as a location phrase), or be part of 住在 + place, but it does not go after 住了 like that.
The usual patterns are:
- 他在这个城市住了三年了。
- 他住在这个城市三年了。

You can’t split it as 住了在这个城市. 在这个城市 must attach to the verb phrase in one of these acceptable ways:

在这个城市 + 住 (preposed location)
住 + 在这个城市 (verb + preposition chunk)

But not 住了 + 在这个城市.

What is the difference between using 住 (zhù) and 生活 (shēnghuó) here? Could I say 他在这个城市生活了三年了?

You can say 他在这个城市生活了三年了, and it’s grammatical, but the nuance is slightly different:

住 focuses on residing / dwelling, having a place to live.
- 他在这个城市住了三年了。
  → Emphasis on living there (having his residence in that city).
生活 means to live (one’s life), to make a living, to go about daily life.
- 他在这个城市生活了三年了。
  → Emphasis on spending life / daily life in that city, not just the physical residence.

In many contexts, they overlap and both can be used. For “He has lived in this city for three years” in the sense of residence, 住 is the most direct and common verb.

Is there any tense in this Chinese sentence? How do we know it corresponds to English “has lived / has been living”?

Chinese does not have grammatical tense like English (past, present, future). Instead, it uses:

Aspect particles (like 了, 着, 过)
Time words (like 今天, 昨天, 明年)
Context

In 他在这个城市住了三年了:

The first 了 after 住 marks that the action has been realized / carried out.
The duration 三年 shows how long.
The final 了 shows the current state is “it has (now) been three years”.

This combination naturally corresponds to English present perfect / present perfect continuous:

He has lived in this city for three years.
He has been living in this city for three years.

Both are good translations of the same Chinese sentence.

Are there other word orders that are still correct, like moving 三年 or 在这个城市 around?

Yes, but with some limits. The most natural variants you will hear include:

他在这个城市住了三年了。
他住在这个城市三年了。
他已经在这个城市住了三年了。
他在这个城市已经住了三年了。

What you generally cannot do:

You can’t break 住了三年 arbitrarily:
- ✗ 他在这个城市三年住了了。 (wrong)
You can’t move 三年 far away from the verb phrase in weird ways:
- ✗ 三年他在这个城市住了了。 (wrong as a normal sentence)

Safe guideline:

Keep 在 + place close to 住, either before it or as 住在 + place.
Keep the duration (三年) close to 住了: 住了三年 (了).

Does this sentence sound natural and common in everyday Mandarin, or is it more textbook-like?

他在这个城市住了三年了。 is very natural and common in everyday Mandarin.

Native speakers say sentences with this V + 了 + duration + 了 pattern all the time, for ongoing situations:

我学中文学了两年了。
I’ve been studying Chinese for two years.
他们在这里工作了五年了。
They’ve been working here for five years.

So yes, your sentence is both correct and authentically used in real life.