Learn Hardcore Portuguese (Portugal): A discussão foi longa, mas no final chegámos a um acordo. - The discussion was long, but in the end we reached an agreement.

You are talking about a specific discussion that both speaker and listener know about (the one you just had), not any random discussion.
In this sense, a discussão behaves like a reunião (the meeting), a conversa (the conversation), etc.

Does discussão mean a neutral “discussion” or a more negative “argument / quarrel”?

Discussão can cover both meanings, depending on context:

Neutral: a structured or serious discussion
- Tivemos uma discussão sobre política. = We had a discussion about politics.
Negative: an argument, often heated
- Tive uma discussão feia com o meu irmão. = I had a bad argument with my brother.

In your sentence, A discussão foi longa is neutral by itself. If it were very negative, you would usually see extra words: foi acesa, foi intensa, foi desagradável, etc.

Why is the past tense foi used and not era? What is the difference between foi longa and era longa?

Both foi and era translate as “was”, but they are different past tenses:

foi = pretérito perfeito (completed past)
era = pretérito imperfeito (ongoing / descriptive past)

A discussão foi longa

Presents the discussion as a complete event in the past.
Focuses on the fact that the entire discussion, from beginning to end, was long.
Fits perfectly with no final (“in the end”) and chegámos a um acordo (a completed result).

A discussão era longa

Would sound odd here; it suggests a habitual or background description (“the discussion used to be long”) rather than one specific event that ended.

So foi is correct because you describe a single, finished discussion.

Why is longa feminine? Shouldn’t it be longo?

Adjectives in Portuguese agree in gender and number with the noun they describe:

discussão is feminine singular (you can see this from a discussão).
Therefore the adjective must also be feminine singular: longa.

Examples:

O dia foi longo. (masculine singular: o dia → longo)
A reunião foi longa. (feminine singular: a reunião → longa)
As reuniões foram longas. (feminine plural: as reuniões → longas)

So A discussão foi longa is the correct agreement.

Is the comma before mas necessary? Could I write A discussão foi longa mas no final chegámos a um acordo without the comma?

In standard written Portuguese, a comma before mas (when it introduces a contrasting clause) is expected and considered correct:

A discussão foi longa, mas no final chegámos a um acordo.

Writing it without the comma:

A discussão foi longa mas no final chegámos a um acordo.

…is common in informal writing (messages, chats), but in careful writing (essays, exams, formal emails) you should include the comma.

What exactly does mas mean here, and can I replace it with porém or no entanto?

Mas means but / however, introducing a contrast to the first part of the sentence.

Possible alternatives:

porém = however / but
- A discussão foi longa; porém, no final chegámos a um acordo.
no entanto = however / nevertheless
- A discussão foi longa; no entanto, no final chegámos a um acordo.

Differences:

mas is the most common, neutral, and natural in speech and writing.
porém and no entanto sound a bit more formal or literary and are more common in writing.

So you can replace mas, but the original version is the most natural everyday option.

What does no final literally mean, and what is the difference between no final, no fim, and por fim?

Literally:

no final = in the final part / at the end
- em
  - o → no (in + the)
- final = end, final part

Subtle differences:

no final
- Often “in the end / at the end (of it all)”.
- Focuses on the final stage or outcome.
- Very natural in your sentence: mas no final chegámos a um acordo.
no fim
- Very similar; in most contexts it’s interchangeable with no final.
- No fim can sound slightly more colloquial or time-based (“at the end (time-wise)”).
por fim
- Means finally / in the end / at last as an adverb.
- Emphasises conclusion more than time.
- Example: Discutimos vários pontos e, por fim, chegámos a um acordo.

In your exact sentence you could also say:

…mas no fim chegámos a um acordo.
…mas, por fim, chegámos a um acordo.

All are possible, with very small differences in nuance.

How does the contraction no work here? Why not say em o final?

Portuguese almost always contracts certain prepositions with the definite articles. em + o is one of the most common:

em + o = no
em + a = na
em + os = nos
em + as = nas

So:

em o final → no final (at/in the end)
em a reunião → na reunião (in the meeting)
em os livros → nos livros (in the books)

Using the non‑contracted form (em o final) is wrong in standard grammar and sounds uneducated.

Why is it chegámos a um acordo and not chegámos em um acordo or chegámos a acordo?

The expression chegar a um acordo is a fixed, very common idiom in Portuguese, meaning to reach an agreement.

Verb: chegar (to arrive / to reach)
Preposition: a (to)
Noun phrase: um acordo (an agreement)

Other options:

chegar em is used in Brazilian Portuguese with places: chegar em casa, chegar em São Paulo.
In European Portuguese, with places you normally use chegar a: chegar a casa, chegar a Lisboa.
With acordo, in both varieties the idiom is chegar a um acordo, not chegar em um acordo.
chegar a acordo (without um) does exist, but is more formal/legal and much less common in everyday speech than chegar a um acordo.

So for standard, everyday European Portuguese, chegámos a um acordo is the natural choice.

What is the purpose of the accent in chegámos? How would the meaning or pronunciation change if it were chegamos?

In European Portuguese, the accent distinguishes tense and indicates stress:

chegámos (with accent)
- 1st person plural, pretérito perfeito (simple past): we arrived / we reached
- Stress on the -gá-: che-GÁ-mos
chegamos (without accent)
- 1st person plural, present: we arrive / we reach
- Stress on the first syllable: CHÊ-ga-mos

So:

no final chegámos a um acordo = in the end we reached an agreement (past event).
no final chegamos a um acordo would mean in the end we (usually) reach an agreement (present, habitual).

In Brazilian Portuguese spelling, the accent is normally not written (chegamos for both tenses), and the tense is understood from context. In European Portuguese, writing the accent in the past tense is standard and helps disambiguate.

Can I change the word order and say No final, chegámos a um acordo or Chegámos a um acordo no final?

Yes, Portuguese allows some flexibility in adverbial placement. All of these are correct, with slightly different emphasis:

A discussão foi longa, mas no final chegámos a um acordo.
- Neutral; the whole sentence flows chronologically: the discussion was long, then, in the end, we reached an agreement.
A discussão foi longa, mas chegámos a um acordo no final.
- Almost the same meaning; the time expression is moved to the end, often used in speech.
No final, chegámos a um acordo.
- Puts strong emphasis on No final (“In the end…”); good if the context has already described the discussion and you are just giving the outcome.

In practice, 1) and 2) are the most common complete versions with the first clause included.

Would Brazilians say this sentence the same way? Are there differences between European and Brazilian Portuguese here?

The sentence is perfectly understandable in both varieties. Common Brazilian version:

A discussão foi longa, mas no final chegamos a um acordo.

Main differences:

In Brazil, you normally do not write the accent on chegamos, even in the past. Context tells you if it is present or past.
Pronunciation will be different (vowel quality, rhythm), but the structure is the same.
The expression chegar a um acordo and no final are used in both varieties.

So only the accent and the pronunciation really differ; grammatically, it works in both.

Are there common synonyms for chegar a um acordo in European Portuguese?

Yes, there are several, with slightly different nuances:

entrar em acordo
- Exists, but is more formal/legal and less common in everyday speech.
chegar a um entendimento
- “Reach an understanding”; slightly more formal.
chegar a consenso / chegar a um consenso
- “Reach a consensus”; often used in group/committee contexts.
concordar
- “To agree”:
- No final, concordámos. = In the end, we agreed.

However, chegar a um acordo is the most neutral and widely used expression for “to reach an agreement” in European Portuguese.

How do you pronounce discussão and chegámos? Any tricky sounds for English speakers?

Yes, there are a few:

discussão

Stress on the last syllable: dis-cu-SSÃO
ç = /s/ sound, like s in see.
ão = a nasal diphthong, roughly like own but nasal: think of “ow” while letting air go through your nose.

chegámos (European Portuguese)

Stress on GÁ: che-GÁ-mos.
ch = /ʃ/, like sh in she.
The final -os is usually very reduced, almost like -ush in fast speech.
The é in che- is often a very short, closed sound, not like English “she”.

Approximations:

discussão ≈ diss-koo-SAUN (with nasal “AU/OWN” at the end)
chegámos ≈ shuh-GAH-moosh (EP, in fluent speech)