Now, what does it mean to have 7th house lord sitting in 3rd house?

It means the planet which rules/controls/owns the 7th house of your horoscope is sitting in the 3rd house of horoscope.

Now, what is the impact of having 7th house lord sitting in 3rd house?

Its generic interpretation is that here energies of 2 business oriented houses are exchanging, so this person becomes very much a business oriented person. It also shows that spouse is bringing lots of business ideas. This also shows that communications are the base of this relation. They want to communicate with each other and lack of communication brings the stress in relations. Spouse may become a Business Partner or vice-versa. As 7th house lord is going 9 houses away from its own house, it shows that your spouse is coming into your life from a far distant place or spouse may be of different ethnicity, as 9th house relates to these things. It also shows that your spouse brings luck to you.

Now, results may be different due to aspect, conjunctions of other planets or the planet being Retrograde or Combust. Moreover, now we also need to check the strength of 3rd house lord as 7th house lord is going in 3rd house. So again, Overall Chart Reading is important.

So, let's see how different planets will behave differently as 7th house Lord in 3rd house.

Sun - Suppose it is a Aquarius Ascendant chart and Sun rules the 7th house with Leo sign and sits in the 3rd house in the sign of Aries, where it is exalted. It shows that your business partner or spouse is a very authoritative person. As Sun is exalted here, the Satvic qualities of Sun will be seen. Here, Spouse will put all the efforts to bring native to that same authoritative state. This may lead to ego battles but the purpose here is good. It shows someone getting great success in Business. At the same time, Sun burns something from the house it sits in. So, relations with siblings may be hurt because of spouse. Here, father may be in a very high authoritative position.

Moon - So it is Capricorn Ascendant Chart and Moon rules the 7th house with Cancer sign and sits in 3rd house in Pisces. This shows that you get a partner who is very emotional and takes care of you like a Mother does. It shows your communications have turned emotional because of the influence of spouse. Here, spouse brings lots of spiritual wisdom and creative imagination to the native. Spouse helps the person to improve his creative skills and pursuits and develop his business.

Mars - Mars can be 7th house ruler through its two signs. So, let's take both one after the other.

Libra Ascendant - So if it is Libra Ascendant, Mars rules 7th & 2nd house and sits in 3rd house in Sagittarius sign. As Mars is in friendly sign, it shows that spouse will have lots of will power and courage to go through challenges of life. Your spouse will motivate you to be brave and courageous. Here, Mars is additionally powerful as Mars is Karaka of 3rd house. Your spouse will be masculine in Physique, even if spouse is a Lady. Spouse will motivate the native to have own business. Here, communications with spouse will be regarding religions, philosophies or higher values.

Taurus Ascendant - Now if it is Taurus Ascendant, Mars rules 7th & 12th house and sits in 3rd house in Cancer sign, where it is debilitated. Here, things are very different. Spouse is getting into communications which are more like Arguments & Fights. Problem with a debilitated Mars is that person only knows that he has to fight, but he doesn't know how to fight? So, same thing goes here. Spouse gets into fight and arguments on petty issues. They want to have their own business but don't know how to do it, hence they try short cut ways and suffer. In matters of Courage, they are Audacious. They can take on a fight which may ruin a life. Basically, they don't know how to balance their emotions and this leads to even physical fights. Again, any other yoga or dasha can change the scenario totally.

Mercury - Mercury also can be 7th house ruler through its two signs. So, let's take both one after the other.

Sagittarius Ascendant - If it is Sagittarius Ascendant, Mercury rules 7th & 10th houses and sits in 3rd house in Aquarius. Here spouse either works in Large Organisation/Large Group of People, away from homeland, where communications are a huge part of work or they work in their own business of counseling, marketing or salesmanship. As Mercury is in a friendly sign, it shows a good communicative relation between couple. It shows that someone might have met his partner through online communication. Here, communications are base of relation. Here, Marriage cant survive without communications.

Pisces Ascendant - If it is Pisces Ascendant, then Mercury rules 4th and 7th house and sits in 3rd house in Taurus. Mercury is again in a friendly sign. Besides the basic requirement of being a communicative relation, this shows that spouse is very analytical & critical and might be in any work related with Finance and Wealth, as Taurus is sign of Wealth. It shows that spouse may be in Finance related Business or in the field of accounting or audit. Other things may be similar.

Venus - Venus also can be 7th house ruler through its two signs. So, let's take both one after the other.

Scorpio Ascendant - If it is Scorpio Ascendant, Venus rules 7th & 12th house and sits in 3rd house in Capricorn sign. Venus is in friendly sign here but as 7th lord is in Saturn ruled sign, it may be a case of delayed marriage. Here, Spouse will be very beautiful. Communications between Couple would be very pleasant. Spouse may be in business related with wealth, beauty and female products and through that they will try to gain authority. Venus in Capricorn shows Love for Authority in simplest sense. So, these people would love to be in authoritative position and they would love to communicate only to people with authority.

Aries Ascendant - If it is an Aries Ascendant, Venus rules 2nd & 7th house and sits in 3rd house in Gemini. This is again a case of energy exchange between two best friends Mercury and Venus. Libra/Gemini and 7th/3rd house all are related to business, it shows that spouse is very much a business oriented person who also brings the same qualities to the native. Spouse will be interested in any business related with Counselling or Wealth/Beauty products. Love towards communications and counselling would be there. Person would be very calculative about his wealth.

Jupiter - Jupiter also can be 7th house ruler through its two signs. So, let's take both one after the other.

Gemini Ascendant - If it is Gemini Ascendant, Jupiter rules 7th & 10th house and sits in 3rd house in Leo Sign. As Jupiter is in sign of its best friend, it shows that person will get a spouse who is very religious and person of high wisdom. It shows regular communication between couple regarding religious, philosophical and issues of higher wisdom. Spouse works like a Teacher or a Guide for Native. Actually, spouse may be a Teacher or a Professor as Sagittarius is sign of Higher Education and 3rd house is house of Communications and Leo is sign of Authority. So, spouse can be working as Teacher/Professor in any School/College. Alternatively, it shows that spouse can work as Counselor on Religious/Philosophical or Education related Issues.

Virgo Ascendant - If it is Virgo Ascendant, Jupiter rules 4th & 7th house and sits in 3rd house in Scorpio. Here, person may be getting married to an Astrologer :). As Jupiter is knowledge, Pisces is Spirituality and Scorpio is Occult, it shows that Person's spouse has great knowledge around Spirituality and Occult. Their daily communications are around the topics of Occult. Spouse may be an Occult Practitioner. Married Life may go through a transformation as Scorpio is sign of Transformation and Sudden Changes.

Saturn - Saturn also can be 7th house ruler through its two signs.

In either sign (Capricorn/Aquarius) as 7th house lord, Saturn in 3rd house (for Cancer/Leo Ascendants respectively) shows that person's spouse may be a Lawyer, more so for Leo Ascendants as Saturn will be exalted in Libra for them. As it rules the house of disputes and exalted in 3rd house of communication, it surely makes a Lawyer. For Cancer Ascendants too, Saturn will be in sign of Virgo which is a sign of disputes and obstacles. Person can be a Judge too. Relations with younger siblings will be a distant one. Person won't have good relations with younger siblings till mid 30s . Likewise, skills and hobbies remain hidden till person attains 30s. After that he will start developing his skills and from mid 30s he ends up having his own work. So, it happens with delay but it happens surely because Saturn in 3rd house person is never able to do jobs whole life. Sooner or later he has to start his own work.

Rahu - If Rahu is 7th house Lord through its sign Aquarius, as it co-rules Aquarius along with Saturn, and sits in 3rd house in Libra then 1st of all we need to make sure of Saturn's position as it is the main ruler. Rahu in Libra in 3rd house will transform Rahu as Venus as Rahu changes its nature as per the lord of sign it is placed in. At the same time, Rahu's basic nature of being insatiable will remain there. Rahu in Libra in 3rd house basically indicates that these people seek ideal relationship life. If they don't see finding it, they prefer not to marry rather than marrying halfheartedly. These people are highly communicative. They are master in marketing. They can sell almost anything and make a business out of nothing. As Rahu rules 7th house, sits in 3rd house in the sign of Libra (which all represent Business), it is most probable that person will be a good businessman.

Ketu - Likewise, If Ketu is 7th house Lord through its sign Scorpio, as it co-rules Scorpio along with Mars, and sits in 3rd house in Cancer then 1st of all we need to make sure of Mars' position as it is the main ruler. As Ketu isolates/separates a person from the things related to the house Ketu is sitting, here it actually separates person from his siblings, either physically or mentally. They never find the balance in relationship with siblings. At the same time, they remain concerned for their siblings. This person may not be too interested in running a business. They may also not be too willing to travel around. Ketu in Cancer also shows someone not getting proper love from mother.