I'm bringing on a business partner. What's a shareholders agreement and do I need one?

What to watch for

Six things that change how a shareholders agreement actually works for established small businesses bringing on a co-owner.

1. The Companies Act default rules aren't designed for small co-ownerships. The defaults bite hardest at exit. When you have one shareholder, the Companies Act defaults are usually fine — you make every decision, you own everything. With two shareholders, the defaults assume an equality and process-formality that rarely matches small-business reality. Decisions under the Act often require ordinary resolution (more than half) or special resolution (75%); a 50/50 shareholding produces deadlocks the Act has no clean answer for. Share transfers are unrestricted by default — your partner can sell their shares to anyone, including a competitor. Issuing new shares requires consideration of pre-emptive rights but the Act's defaults are minimal. A shareholders agreement (alongside a tailored constitution) overrides these defaults with whatever rules actually suit your relationship.¹ Without it, the Companies Act decides what happens when you and your partner disagree, and the Act's answers are designed for the average case rather than yours.

2. Constitution vs shareholders agreement. Different documents, different jobs. A constitution is a public document filed with the Companies Office — it governs the company itself (powers, voting majorities, share types, transfer restrictions, things the company can do that the Act doesn't permit by default).² A shareholders agreement is a private contract between the shareholders — it governs the relationship between the people (who decides what, dividend policy, exit mechanisms, dispute resolution, non-compete commitments, what happens on death or incapacity). The two work together: the constitution gives the company the legal flexibility to do certain things; the shareholders agreement governs when and how those things actually happen. Where the two conflict, the shareholders agreement generally takes priority because it's a private contract between the parties.³ For an established small business bringing on a co-owner, you almost always want both — and the shareholders agreement is the one that does most of the protective work for your specific situation.

3. The control questions matter most when the percentages aren't simple. 50/50 is the hardest case. Share-ownership percentage determines voting rights by default, which determines control — 51% gets you most decisions, 75% gets you the big ones (constitutional changes, major transactions). 50/50 produces a deadlock structure that needs explicit resolution mechanisms in the shareholders agreement, otherwise the company becomes ungovernable when you disagree. Common mechanisms: chair's casting vote on operational matters; mediation followed by binding arbitration for fundamental disputes; shotgun clause (one party offers to buy out the other at a stated price; the other party can accept, or buy out the first party at the same price); or pre-agreed exit triggers. For non-50/50 splits, the minority partner typically wants protection against the majority's ability to make unilateral decisions on things that affect them — major transactions, new share issues, change of business direction, dividend policy. These get protected through reserved matters clauses requiring both parties' consent regardless of shareholding.

4. Exit mechanisms are the most important and most often missed. Address them before they're needed. The single thing most small-business co-ownerships fail to address upfront is what happens when one of you wants out — or has to be out (health, family, bankruptcy, death). Without an exit mechanism, the departing party's shares typically end up either unsold (the remaining party can't afford to buy them at fair value, but neither can anyone else, so they sit in limbo) or sold to a third party the remaining party didn't choose. The exit mechanisms that protect both sides: pre-emptive rights (departing party must offer the shares to the existing shareholders first, at a fair-value mechanism); valuation methodology (how the fair value gets determined — accountant's valuation, agreed formula, independent expert); payment terms (lump sum, instalments over time, with security); and trigger events (what counts as an exit trigger — voluntary departure, prolonged incapacity, death, breach of agreement, retirement). Setting these mechanisms when the relationship is healthy is dramatically easier than negotiating them when one party is leaving in difficult circumstances.

5. The "bad leaver" question. Different treatment for different ways out. Once you have exit mechanisms, the next decision is whether all exits get the same treatment or whether different circumstances produce different outcomes. The common framework is good leaver / bad leaver. Good leaver: voluntary departure on agreed terms, retirement, incapacity, death — shares valued at full fair market value, paid out on agreed terms. Bad leaver: breach of the agreement, dismissal for cause, competing with the business, dishonesty — shares valued at a discount (often book value or a percentage of fair value), paid out on less generous terms. The framework only works if the trigger events are defined clearly and the agreement specifies the valuation methodology for each category. Without good-leaver/bad-leaver distinction, a partner who breaches the agreement (e.g., starts a competing business while still a shareholder) walks away with the same valuation as one who departs honourably. The mechanism is worth getting right.

6. The agreement isn't paperwork. It's the conversation you should have anyway. The substantive value of negotiating a shareholders agreement isn't the document — it's the conversation the document forces. To draft the agreement you have to discuss control, exit, dispute resolution, dividend policy, salaries, working commitments, what happens if either party stops being able to work, what each of you expects from the other. Many small-business partnerships fail because these conversations never happen at the start, and the assumptions on each side turn out to be different when the relationship is tested. A good drafting process surfaces those differences early — when they can be resolved through negotiation rather than litigation. The cost of a properly-drafted shareholders agreement is usually $2,000-5,000 with a lawyer; the cost of not having one and then needing to litigate a partnership dispute is typically 10-100x that. The economics are overwhelmingly in favour of having the conversation upfront.

A separate point on what the shareholders agreement actually protects against. Most small-business partnerships don't fail because one party is dishonest or malicious — they fail because the parties had different assumptions about what the relationship would be, and those assumptions only surfaced under stress. The agreement is the mechanism for surfacing the assumptions explicitly, getting them onto paper, and having a shared reference point when later disagreement arises. It also creates the structural shape for managing the unavoidable changes — one party's life circumstances shift, the business pivots, a new opportunity arises that needs co-investment, a major customer leaves. The well-drafted agreement provides the framework for handling those events; the absence of an agreement forces ad-hoc negotiation under stress. For an established sole operator considering bringing on a co-owner, the agreement isn't just legal protection; it's the operational discipline of having had the difficult conversation while the relationship is healthy enough to support it.

Where this entry stops

This entry covers the shareholders agreement framework for established small businesses bringing on a co-owner. It doesn't cover:

• Startup-specific shareholders agreement provisions — founder vesting schedules, investor protective provisions, drag-along/tag-along for VC rounds. Different audience; well-covered by startup-focused content.
• The mechanics of issuing or transferring shares — share certificates, share register updates, Companies Office notifications. Procedural; Companies Office covers it.
• Tax implications of share transfers — buying out a partner has tax-side consequences for both parties. Accountant territory.
• Partnership Act 2019 for unincorporated partnerships — different statute, different framework. If you're not in a company structure, the analysis is different.
• Adding a co-owner once the business is well-established and the new party brings capital or specific expertise — see the entry on adding a co-owner or partner for the decision side, with this entry covering the documentation side.

For drafting the agreement itself, a commercial lawyer is the right resource — template-based services (LegalVision, Sprintlaw, On Your Terms) work for straightforward cases; complex cases (significant assets, asymmetric contributions, family-business dynamics) need bespoke advice. The cost-benefit is overwhelmingly in favour of professional drafting given the downside exposure.

Last verified 11 May 2026. Full source list: references.